They were wrong. Not the Mayans, but the people who hung their beliefs on the notion that turning a page on a calendar (all right, a rock, but it's the same principle) meant the end of the world.
If you want to write, you need to be aware of the end of the world - or, more accurately, of milestones you must pass.
Getting your first bad review is crushing. Especially if it's from some nameless person on Amazon.com. However, it's not the end of the world. As Mr. Nelson put it, you can't please everyone, so you've got to please yourself. Write the books you'd like to read.
Learning that your book has earned a pittance is crushing, but it's not the end of the world. Realize that writing a book is not the end-all. It's a step on a career. There's another one to be written, and one beyond that, and slowly your audience will build.
Getting a rejection letter from a publisher - especially one of those horrible form rejections - is crushing. You feel worthless. But it's not the end of the world. You failed to hit it off with ONE editor at ONE publisher. There are more fish in the sea, and these days more ways of publishing your work.
Having writer's block is crushing. You feel miserable. You'll never write again. Why go on? But it's not the end of the world. Writer's block is common and it's self-curing. What it generally means is that subconsciously you're working out problems in your story, and when that process is churned through, the words flow again.
Take heart. We're still here. The sun goes on shining, the sea rushes to shore. Hey, it's not the end of the world.