I guess it's just a combination of circumstances; being in the right place at the right time; being in a certain vulnerable state of mind where the events and emotions the characters go through start influencing me to such an extent that I enter the kind of space where there's only me and the movie, nothing else exists around me for the duration of the movie.
I don't become one specific character, I feel that I'm an invisible observer, able to experience the emotions of every character and the dynamic between the characters and sort of live through their experiences and every possible emotion they portray on the screen.
It's an emotional rollercoaster and it's not about the sadness of the movie or happy endings, and I certainly don't cry during every sappy movie out there. As I said, it has to be a combination of things to get me to that point where the emotions just become too much to keep them inside and it doesn't happen very often.
Mar Adentro and Dancer in the Dark come to mind at the moment. There are others, of course, but these two have stuck with me for years now. The helplessness and injustice the main characters had to go through and the emotions that accompany all that just create this tension that I can't avoid during watching them and it has to find its release one way or the other. Crying helps.
I was never really one to cry during movies, but now I'm finding myself doing it more frequently than ever. I've always gotten teary eyed during tv shows like Extreme Home Makeover, and other programs where people experiencing severe hardship get the pleasant surprise of a lifetime. There's something about seeing the ideal of human altruism and potential manifest itself in real life, and I find those types of things especially moving. The movie Up really had me going, and The Last House on the Left disturbed me to tears.
There is a thinking stuff from which all things are made, and which, in its original state, permeates, penetrates, and fills the interspaces of the universe.
There are a few specific scenes that will do it for me.
One is in The Patriot, where Benjamin Martin is getting ready to ride off to war one more time, and his youngest daughter, who hasn't spoken since her mother died, is watching him go... suddenly she breaks away from her aunt and runs after him, saying "Papa! Papa, don't go, I'll say anything! Please, papa, I'll say anything you want!"
The other is a scene in Shadowlands in which an almost uncannily reserved Anthony Hopkins, having been through the terrible lengthy ordeal of his wife's painful death from bone cancer, just loses it... and I mean loses it.
I tear up again just thinking of the scenes, even though I know outright that I'm being manipulated. Doesn't matter, it still works.