You should be able to look back at the person you were two years ago and think of something you did or believed that would make the present you say, "Man, what a moron." In short, if in the span of two years you can't become a noticeably better person (at least in your own eyes) then you are doing something very wrong with your life. Here is a very incomplete example list from my own life.
Age: Misconception. Lesson Learned.
22: Present day.
20: Believed success could be achieved in the absence of opportunity by working hard enough. The opportunity must be sought out before the work begins!
18: Took rewards for granted; Believed that rewards will come to people who deserve them. You will be given little or nothing if you don't have the audacity to ask for more.
16: This was the climax of my personal change from Boy to Man. The amount of personal change, for both better and worse, could not be described in a thousand books. Whatever faults I had or lessons I learned in this time period are so fused with subtle mental changes caused by puberty that I cannot distinguish one from the other.
14: Believed that I had figured out how the universe worked, understood God, and knew the meaning of life. In reality, a lot of what I "believed" were things that I just wanted very badly to be true, so I convinced myself that they were. We must acknowledge that some things will forever be beyond our understanding.
12: Believed anything I was told by a generally trustworthy source, backed by the common child's perception that adults have almost god-like intelligence and practicality. Adults, even trustworthy ones, can be just as stupid as children.
Updates will be unreliable until around the middle of September, when I can find a good rhythm for my schedule-ruled life. I despise schedules, someday I must create a society that doesn't need them.