I want to write a book that's encouraging, and I have the first chapter, which is a little encouragement on just being alive.
It's 800 words, and I'd like to upload/post it on some web, blog, or forum to see what people think.
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I love Medium. It's a great site to read short and long essays.
Try http://hubpages.com/ -- previously squidoo.com Pick the proper category and publish your article there for free and maybe generate a lot of interest.
Here's a good article which will provide you with more places where you may be able to publish articles like this: http://www.lifehack.org/articles/work/20-websites-you-cant-miss-you-want-make-money-freelancer.html
I was about to suggest Medium, but since it's already proposed by @Lehi, here is another place to share your thought: Thought Catalog an independent digital magazine.