Every time you read a post and you think about what the post means, or how the post works, you gain experience. That is why classroom learning works.
in reply to How can this be?
If you see it enough, or you read it enough, it will stick, and the next time that you are faced with a similar situation that someone else posted about, you can say
Chromatic showed us we can do it this way, so I am going to use that, or BBQ posted this snippet, and if I modify that way then I can use, and you're on
your way to 'real' XP. Part of gaining Monk level is just showing up and absorbing the information on the site.