It needs to draw upon the things that we bury deep within ourselves, things that aren't discussed in polite company. The best cartoonists know how to drag out the worst parts of themselves and smear them on paper for the rest of the world to see. Sure, a cartoonist can put a cute spin on things, draw adorable animals and little children, appease the family-friendly syndicates, but in the end, the thing that makes for an effective gag is the cartoonist's ability to neatly package the worst things about humanity and leave them on your doorstep in a flaming paper bag. It can be highly traumatic. Often, it's a bit of one, half-dozen of the other.
Sanity depends on it.
But the cartoonist continues to do this on a daily basis, which makes me think, some days, that we must be a strange breed of masochist. The undisputed master of cartoon humor was Charles Schulz. He created the archetypes of cartoon characters that the rest of us can only hope to imitate in our own flailing, pale manner. I see bits of Charlie Brown in Jon, bits of Snoopy in Toothgnip, bits of Lucy in Diablo. And the greatest compliment I can think of to receive would be if someone emailed me a nasty flame telling me how unoriginal I am, because that would mean that I had managed to steal even a little bit of the man's brilliance.