We have a lot of folk wisdom in the dojo. "Keep blood in your skin sack". "It's always your turn". "Hard weapons=soft targets". But I think my favorite is the one we aren't allowed to say "I can't". If you say those words on the mat, you'll quickly find yourself doing push-ups but you'll also have an instructor right there to talk to you to phrase what you really mean. It could be that you think "This is really hard" or it could be "I have no idea what you mean". These two statements are very different and making the distinction between them will allow your training to progress. The words "I can't" stop all future growth; you just stop dead and now you start trying to prove how you really can't. You can. Maybe not today or even tomorrow but if you keep trying eventually you'll say "I did it"!