Think about a time when you were badly disappointed. Then think of any opportunities you had previously, to notice that things weren't going to turn out the way you'd expected. In particular, cases where you came across an argument or evidence that in hindsight should have changed your opinion, but you dismissed by a clever argument, or by not thinking about it.

Think about what you could have done in the time you had between your missed opportunity and the disappointment. Plans you could have changed to make the best of a bad situation. Mentally contrast the actual outcome with the outcome had you been forewarned, and allow yourself to be very annoyed at your past self for throwing away time.