Keeping a journal is a really good idea. Quite aside from the discipline
it gives you and the delightful consistency
of turning to the journal on a regular basis, no matter what's going on in your life, it serves as an important historical record
of your life. Things you think you're always going to remember
actually fade. You might not forget that your brother won an Academy Award, but you might forget how his brow furrowed when he got the call that he was nominated, and how you, being his sibling, immediately knew what was going through his head -- "Who, me?" That's the kind of thing a journal can preserve.
If you need to you can go back in time and read not only what you wrote, but how you wrote it -- your diction, perhaps using a word you don't use anymore; your very handwriting, perhaps shakier, perhaps bigger, bubblier letters, perhaps caffeine-scratch at a cafe -- and put yourself into your old shoes. I tell you, it's better than therapy.