Don't you hate it when the momentum train that you are on is building you up, pushing you over that obstacle, enlightening you and then something small derails that train. That something small was the word you didn't want to correct. Okay, it may seem extreme, but that is people feel when your spelling is subpar. It chips away at the very best message you were sending across, even though it may be only one word.
Im sure you have seen posts across Facebook, Twitter, Reddit, Imgur, with the edit comments: you're*, they're*, Battlefield Counterstrike* (Long story, I dare you to find it on Imgur) and it is endless. Your message that was being sent across has now become a tangent of internet cats, spelling badly GIFs, and Michael Cera. Crazy, but it happens.
When you look at a post from someone that has a lot of followers or even that multi-billion dollar company, you will see that they spell-check everything, have another editor/person proof-read it, or even put that 5 paragraph message into Microsoft Word and look for all those red lines. You should too. If you want that message to be sent across correctly, igniting that spark between what you write and that person's emotions, grammar is KEY.