D EAR HARRY: My father always thought of you as the greatest invention since aspirin. He bought some Berkshire Hathaway stock all through the '80s at your suggestion. You must know how well it performed. He recently died and left me his 10 Class A shares. I am married and doing quite well financially for a guy who's 58. I'm a senior engineer for a company that treats its people well. I have a solid salary, great pension, and every kind of insurance imaginable. My children are all out of the home (except for a 6-year-old Lab retriever) and doing well. We have zero debt. The problem is that the Berkshire stock is more than half my total assets. My company's treasurer recommended that I diversify by selling all but three shares and moving the money to mutual funds. What's your take?