Thanks to Writer's Digest, from a short piece a few years ago . . by Miryam Williamson. The focus and title of the short lesson, I think, perfect for cartoonists was: ZEN AND THE ART OF PERSISTENCE.
I keep a copy of it handy when outside forces and other people's opinions have a way of creeping in to try to rain on your parade . . article went . .
ROBERT PERSIG sent ZEN AND THE ART OF MOTORCYCLE MAINTENANCE to niney-two publishers before it found a home . . you read right . . 92 publishers before it found a home. I wouldn't believe it if I hadn't heard him say it myself ( On NPR, not to me ). You and I should be so unsuccessful.
Keep on sending that manuscript out. Have a plan to send it to someone else when and if it comes back. Make a list and work your way through it. Don't let a returned manuscript sit on your desk for more than 24 hours. Don't give up. There's a publisher for every book that has a writer's skill and love in it.