Lifted from the Inception wiki
Gordon-Levitt asserts, “Arthur is the organized one, the one making sure everything is in its right place. The way I see it, Cobb is the artist and Arthur is the producer. He’s the one saying, ‘Okay, you have your vision; now I’m going to figure out how to make all the nuts and bolts work so you can do your thing.’ But as fastidious and professional as he is, Arthur didn’t want to apply his organizational skills to being a lawyer or doctor or any of the things he could have been because sharing dreams is fascinating. It’s not just a job for him. I think the technology of dream sharing is something that has inspired him since he first heard about it so, ultimately, it’s not the money he’s doing it for. He wouldn’t risk his life for a good paycheck. He loves it.”