"I didn't really know anything different," Castillo said.
That raw effort and capacity for work has sustained a football career that began in a small town near the Mexican border and has led to the Eagles defensive coordinator job.
But hustle and drive alone don't erase the huge question looming over Castillo's recent promotion: Can the Eagles really expect a defensive revival from a man who spent the last 21 years on offense? With its high-scoring ways, the team has Super Bowl hopes. But it has turned the defense over to a man who last coached on that side of the ball at a Texas high school in 1989.
If you ask Castillo, 51, how he'll overcome the skepticism, he tells his life story. And if you ask him about his life story, what emerges is his argument for why he will succeed.
"All my life has been about challenges," Castillo says, and he tells you about them.
Tore up the table
Castillo's parents, Gregorio and Juanita, were born in Mexico and moved to Port Isabel, Texas, as teenagers. The town sits on the Gulf Coast, practically at Texas' most southern tip. Just a few thousand people lived there, many of them Mexican immigrants attracted by jobs on shrimp boats.
Gregorio shrimped. Juanita was a maid in hotels on nearby South Padre Island. Juan was the oldest of three children, and the only boy. Shortly before he entered sixth grade, his father fell off a boat into the Gulf. He was never found.
His mother took on a second job busing tables. She never dated, Castillo said, just worked and made a hot breakfast every morning.
"She was special," Castillo said.
As in much of Texas, community life in Port Isabel revolved around high school football. Friday nights everyone came out to see the Port Isabel High Tarpons play. Castillo dreamed of standing before his cheering peers at pep rallies.
"If you played football, everybody knew who you were," Castillo said.
He poured his work ethic into football. The summer before his senior year he bused tables and worked in a local grocery store. He bought a barbell with his earnings and squeezed in training at night, using a living room table as a bench. Workouts began at 11:30, and continued for 90 sweaty minutes.
"That table got torn up a little bit," Castillo said.
That year he made the 2A all-state team as a linebacker.
"That's where it started," Castillo said. "If you work hard, good things happen."
Castillo, however, had no big-time colleges sending him letters. After a semester at Monterrey Tech, he transferred to Texas A&I, now Texas A&M-Kingsville.
After working out with his teammates, Castillo would sneak back to the track, making sure no one saw him.
"I found out, if you want to be better than someone, you've got to outwork them," he said. "How can you beat a guy or be better than a guy if you're doing the same work he is?"
As a junior, Castillo started at linebacker on a team that won the NAIA national championship. But his playing career ended after his senior year - without a degree or a plan. He went back later for his degree but immediately began his education in coaching.
Anyone who has ever attended an Eagles practice has heard Castillo's voice. In team drills, the coach, then for the offensive line, races into the mass of tangled bodies, exhorting his linemen to attack.
His unit is the last to leave, his men repeating the same steps, the same hand placements, over and over, bursting out of stances and into pads held by teammates. Each repetition he punctuates with a "Boom!"
"He's a contradiction," said Fred Nuesch, a former A&I sports information director. "He's very soft-spoken and extremely polite, but when it comes to playing and coaching, he's extremely aggressive."
Castillo's attitude with the Eagles is actually toned down, said retired lineman Jermane Mayberry, who played under Castillo at A&I and with the Eagles. "He was crazy intense" at school.
Shortly after college, Castillo, trying to catch on with semipro and USFL teams, took a series of A&I assistant jobs under his old coach, Ron Harms. Early on, he was assigned an unruly group of defensive linemen not much younger than he was.
Seeking to establish his authority, Castillo challenged them to boxing, going one-on-one for 60 seconds apiece. He made it through four before one tackled him and sprained the coach's ankle, ending the session.
"I was young. I didn't know that you earn respect by teaching," Castillo said sheepishly. "I was like, 'I'm going to teach 'em. We're going to mix it up.' "
As he shuffled between assistant coaching jobs at A&I and the USFL, Castillo began to pair effort with technical precision. With the USFL's San Antonio Gunslingers, for whom he played in 1984 and 1985 in between coaching stints, he learned how to use his hands on defense. He taught his A&I linebackers by challenging the offensive linemen to try to block him.
Castillo describes a confrontation like choreography: Lead step, shoot your hands, roll your hips, lock 'em out, torque 'em.
Castillo demonstrates as he talks, crouching before firing his hands upward into a listener's armpits and then extending his arms straight, creating distance between himself and his man, a position from which he can steer even a larger player.
When Harms found out about the impromptu boxing session, though, he wasn't happy. According to Castillo, the coach wanted him out. Harms said he knew Castillo's USFL playing days were numbered and wanted the young man, who now had a son, to get a better-paying job and support his family.
In either case, Castillo landed at Kingsville High School, where he would learn a more refined way to coach and set in motion the first big switch of his career.
'I'll learn it'
At Kingsville High, Castillo had far younger students. Instead of challenging him, they admired him. Their girlfriends chatted with his wife, Zaida.
One of his players was Harms' son, who relayed Castillo's effort and maturation to his father. Four years after leaving Texas A&I, Castillo was asked back. Harms wanted the former defensive coach to lead his offensive line.
To Castillo, it was a dream opportunity: a chance to return to his alma mater for a full-time job. He gushed the news to his wife.
Offensive line? Zaida asked, "Do you know that?"
"I said, 'No, baby, but I'll learn it.' "
Harms said he believed Castillo's work ethic could make the unusual move a success.
"Coach Reid obviously has the same feeling about Juan as I did," Harms said. "He's the hardest worker I've ever seen, period."
Castillo studied for his new job, following the advice of a friend in business: by finding outstanding examples in the field and following their lead.
On spring break, when the school paid for one flight and three per-diems to let coaches study other staffs, Castillo stretched the opportunity into two weeks of learning. He'd fly to Indianapolis, rent a car and drive to Washington and Buffalo, back to Chicago, Notre Dame and the University of Michigan, absorbing knowledge from coaches at four NFL teams and two big-time colleges. To save money he slept in his car and drove overnight.
If he could coach his small-school players into the NFL, maybe he could follow them.
Technique and toughness
At Texas A&I, practice began at 3:50 p.m., but Castillo had his men on the field at 3. He wanted them focused on technique, so it would come to them naturally in the heat of a game. He stressed details. Placing a hand on the outside of a pass rushers' number instead of the inside could make the difference between success and failure, Mayberry recalled.
Castillo also demanded toughness. But he thought his line was soft. So before games, he sometimes head-butted his helmeted players until his bare forehead bled.
In practice, he insisted they chase the play and hit until the whistle - or later.
Their aggressiveness became so pronounced that a defensive coach hauled Castillo into Harms' office: The offensive line, he complained, was going to hurt someone. Castillo recounts the accusation with pride.
"One of the most awesome things that happened to me," he said.
Another big chance
Four of Castillo's proteges, including Mayberry, made it to the NFL. Castillo landed with the Eagles in 1995 as an offensive assistant, hired by Ray Rhodes after he had internships in three NFL cities. He stayed on when Andy Reid came aboard and in 1998 became the offensive line coach, a job he held until a few weeks ago.
He brought his trademark focus on technique and effort but with a milder personal touch. Before games, he said, he simply sits with his linemen in the locker room.
"I just want them to know I'm here," Castillo said, though he admitted to head-butting tackle King Dunlap once or twice.
He has four children, all boys, who also receive his particular brand of coaching.
"When he's not working, he's all about his family," Mayberry said. "Doesn't have hobbies, doesn't golf. . . . He trains his boys."
His oldest son, Greg, is 20, a junior cornerback at Iowa. His second son, John, 19, is a distance runner at Villanova.
Castillo said he'll soon turn his athletic focus toward Andres, 13, and Antonio, 8.
When Castillo interviewed for the defensive coordinator job, he met Reid at 4 a.m., likely to keep the talks under wraps, Castillo said. It was the same hour he'd arrive at the fish house in Port Isabel. He earned another big career switch. After nearly 30 years in coaching, he became an NFL coordinator.
This time, Zaida greeted him with a big hug, but Castillo was subdued.
"This is what I've been working for," he recalled in a whisper. "Now it's on."
Castillo has stepped up to a plateau few Hispanic coaches have reached. The Panthers' Ron Rivera recently became just the third Hispanic head coach in league history. Castillo, who was honored in Port Isabel with Juan Castillo Day on July 4, 2009, said he hopes his story inspires others from his home and other Mexican-Americans.
"I want them to know that anything and everything is possible," Castillo said. Along with his coaching success, his youngest sister, Janie, is set to soon become a doctor. "Coming from two parents that didn't even go to school. Anything and everything is possible. You have to have a plan . . . and the plan consists of a lot of hard work."
It will be months before anyone can say whether promoting Castillo was the right move, but for now, the Eagles have expressed confidence, based on his past.
"I've learned the hard way to never bet against people who always find a way to succeed," Eagles president Joe Banner said. "The essence of who Juan is is somebody who finds a way to overachieve and find ways to be successful in whatever he does."
The Eagles are betting on him - and betting big. Castillo said he'll prove them right. He expects it will take a lot of work, but he's used to that.
Contact staff writer Jonathan Tamari at 215-854-5214 or email@example.com. Follow him on Twitter at twitter.com/JonathanTamari.