It's my passion. I've had tanks for as long as I can remember. And although they can be frustrating and time and money consuming, in the end, the pleasure that I get out of it, is worth it all. Some people spend money to go on vacation, others spend money on drugs, alcohol, etc, I spend money on my fish. Everyone needs to have a joy in life. I can sit in front of my tank after the worst day, and feel at peace (until I see a coral knocked over, etc, LOL). And, let's all be honest, we love that "Wow, that's amazing," that you get from guests that come in your house and see your tank(s).
And then there are the wonderful hobbyists, both online and in my local reef clubs. They're like family. They're more willing to help out when you're in need than your own family and friends most of the time. Great people in this hobby, and even when I'm most frustrated, they keep me in it.