I LOVE this scene. The philosophy that Yoda is teaching Luke here is truly inspiring. It's a good parallel to our own world. Everyone nowadays is so caught up in what they think they "can't" do.
Take Luke in this scene for example. He sees a seemingly hopeless situation and instead of thinking positively and believing that there's a way to get the x-wing out of the pond, he immediately gets discouraged and doesn't even think to try.
Then Yoda spits his wisdom and opens his mind to new possibilities, and shows Luke that everything he perceives as impossible is purely mental, and he can go as far as his mind lets him.
That's honestly a very refreshing and motivating thing, I think we could all use Yoda's advice in this scene. Obviously none of us is a force wielding Jedi, but we can always choose to look at a hopeless situation in a more positive light, and with this we can all achieve our full potential and, in a sense, become a true "Jedi" just like Luke here.
'Do or do not- there is no try' is one of the best advises you can give someone who wants to accomplish his dream, his goals, his purpose.
Forget about mentally psyching yourself out, just have some faith and DO.