Did Thomas Edison really say it?
I have not failed. I've just found 10,000 ways that won't work.
Really: Walter S. Mallory, recalling Edison, 1910
Edison did say something like it, but in other words. A 1910 biography quotes him: I know several thousand things that won't work. The 10,000 version came later.
How to post it: Use the documented version, or say paraphrasing Edison.