Yea that's the whole point - positive effect in your life and possibly in others as well. You can enter by just simply stop complaining for the next 21 day. haha If you do enter - and you wanna spread the word (positive effect), just simply let others know that you are doing this - it can be a post, video etc. whatever you want.
Hope to see your posts about #21daynocomplaint around!
Cheers!