"So often we try to make other people feel better by minimizing their pain, by telling them that it will get better (which it will) or that there are worse things in the world (which there are). But that’s not what I actually needed. What I actually needed was for someone to tell me that it hurt because it mattered. ...I find that it is a lot easier and more bearable to be sad when you aren’t constantly berating yourself for being sad." -http://fishingboatproceeds.tumblr.com
It makes me sad to think that John liked the idea of telling sherlock he isn't always right, but he probably never imagined saying it while being proud of Sherlock and at the same time wishing it wasn't true.