I can remember a time when I was younger that we finished watching a movie as a family and looking back, I could see that my mom had been and maybe still was crying. In my child mind, tears mean sad or hurt and it was a happy ending. When I asked my mom about it, she told me that I'd understand someday, and more unbelievably, that I would cry like that myself one day.
In college, I remember thinking back on that, and ha, I rarely teared up at the end of movies.
Now however, it's often :) A good ending, maybe not even an ending, a touching commercial, a sweet story, just watching Sam play and smile sometimes. Life changes us.