I vaguely remember reading this book title, one of my dad's books: learn, unlearn, and relearn.

I guess that has to be done with friends you don't meet for a certain period of time. Especially friends whom you had a negative perception towards. When you meet them again (if ever), you'll have to unlearn what you learnt about them in the past, and relearn things about them. If people do change, then so should our perception of people. ;) (I think that we usually have a fix perception of a person, if we do not hear any updates from them.) Not an easy thing to do, but it increases brain activity, and allows you to look at things in a fresh perspective. :)