We all make mistakes, and many of them are likely to be financial ones: bad buying, bad borrowing and failure to save, among others. Deciding to learn from those mistakes is the best policy.
Failure philosophy. Under the heading "A philosophy of failure," J.D. Roth writes at his getrichslowly.org site that we can learn from "mundane mistakes" such as going food shopping while hungry. He's got a three-step plan in this post. First, figure out what went wrong. The second step is to make a plan to prevent the mistake. Perhaps, for example, you need to make a point of having a snack or meal before you get to the grocery store. And, third, "view each mistake as temporary and isolated." That way, the "failure" is not part of a larger, more difficult problem, like a character flaw.