Seinfeld's not the only one who thinks writers should stop making excuses. Steven Pressfield's book, The War of Art, is a master class in combating "Resistance" — his term for the cumulative forces (both internal and external) that aim to prevent us from doing our work.
Here's what he has to say on the matter (emphasis mine):
“Resistance will tell you anything to keep you from doing your work. It will perjure, fabricate, falsify; seduce, bully, cajole. Resistance is protean. It will assume any form, if that’s what it takes to deceive you. It will reason with you like a lawyer or jam a nine-millimeter in your face like a stickup man. Resistance has no conscience. It will pledge anything to get a deal, then double-cross you as soon as your back is turned. If you take Resistance at its word, you deserve everything you get. Resistance is always lying and always full of shit.”
Another good quote:
“There’s a secret that real writers know that wannabe writers don’t, and the secret is this: It’s not the writing part that’s hard. What’s hard is sitting down to write.”
This sort of thing is a common theme I see from creative people who are at the top of their respective fields. Yes, there are days when it's more difficult than usual to produce something great, but none of that takes precedence over sitting down and doing the work.
My advice is to listen to these guys. They certainly didn't get to where they are in life by being lazy.