Imagine you are putting money down on a fighter. You analytically look at his (or her) record. You examine his or her style of fighting. You know which punch he or she uses most often, and what little tricks (like rope a dope) she or he has. You like the fighter's record; you like the fighter's devotion to the sport. You even kind of admire the fighter. But even with the money down, you are not truly and purely emotionally invested in the win. From an intellectual standpoint, yes; but emotionally, you're still on the outside.
The day of the fight comes; your fighter is getting beaten badly. Not from the opponent. They're pretty evenly matched. But from the audience. Cups are flying. Peanut shells are hitting the fighter (miraculously, only your one), and the opponent is getting a few good hits here and there. Now, some fans who were rooting for your fighter have crossed lines and are rooting for the other fighter. Some fans are now rooting for your fighter mostly because of the peanut shells and the cups, and the amount of trash being thrown. And some fans are still with their fighter, because he or she has done very little wrong and certainly didn't tell the audience and refs to throw shit. But you are now emotionally invested in this fight in a way you hadn't been previously. Now, you want your fighter to win, and you want them to win badly. Your allegiance is intensified because of the amount of shit your fighter has to deal with in addition to fighting the actual fight. You didn't come to the fight thinking, "Well, trash is going to get thrown because (insert reason here), so I'd better support them." Your reasons were already set in stone. But actually and fervently and passionately wanting to see them win stems from this; it is merely icing you neither anticipated nor wanted on the cake you'd been eating.
That is why I ardently supported Hillary Clinton, and why I'm now becoming more and more aligned with Obama. In the beginning, I could honestly say that I liked their positions. I'm socially liberal; and I'm a pump-primer as opposed to a trickle-downer. Plus, McCain's "Bomb Iran" song scared me. But with the crap Hillary dealt with in the primaries, I desired her win partially to shut up those who would malign her based on her gender and who worried about her cleavage or wrinkles or menopause - or even how she reached the upper levels of politics (that one irritates me because it isn't like she married a Kennedy or a Bush or a Rockefeller; she married a guy from Arkansas whom she then assisted in his own political aspirations). But I had wanted her to win before. Now, Barack Obama is ahead of John McCain in the polls; but the "baby momma" stuff on Fox News, the Obama Bucks, the monkey dolls at McCain rallies, etc., makes me want him to win all the more. I want him to win, because I've always wanted him to win. But now, I want him to win even more. It is unexpected icing on an already-baked cake.