I just realized how brilliant this movie was
I saw the first 20 minutes, had no clue what was going on... too many random scenes with random people... and then we're sorta thrust into 3 different stories, all revolving around love, relationships, truth, lies, memories, destiny... and then I went back and saw the first 20 minutes again, and now it all makes sense! All those scenes at the beginning were the memories that he talks about throughout the film. The friend at age 12 going away, the girlfriend at age 17, the medical student who hated her teacher, talking to his father, etc.
It's frustrating watching something like that for the first time, because it's difficult to understand what's going on and what the significance is, because you don't really think about it later on. But then, once I saw it again, I realized how amazing that intro is. The whole movie is brilliant. Totally underrated.