The hours are long, the deadlines are tight, the work is demanding, and some of the egos involved are unbearable. For the most part, however, you're doing what you love to do and you're making magic happen, which makes up for a lot of the icky parts.
Some of the most stressful moments can arise out of differences of opinion with the director. Remember—you're an artist, not a laborer; yet the director has final say on all decisions. So while you may want to use the red-orange gel for the sunset, if the director has green stuck in his head, then green it is. You can argue your case, but you have to give in when you meet resistance. If the move works and the film is a huge success despite the difference of opinions, both of you will be able to ride off together into the green sunset.