Yoda's quote doesn't make a great deal of sense. Imagine this convo between Luke and Yoda:

"Okay... I shall try to punch through this wall."
"Do or do not, there is no try."
"..." Luke punches the wall but fails to punch through, and he grimaces in pain.
"And so you did not punch through this wall."

Whee. Promos in 18 hours time. GG.