You can do it

Famous motivational quote (even my school uses it), but not really. It's kind of like instilling optimism without evidence: it likely won't work.

"You can do it" is logically meaningless

Because while it technically is true, it is already implied: if someone cannot do something like flying, nobody would demand or even expect them to fly… And it doesn’t even work as encouragement anymore due to the overjustification effect, and thus feeling a sense of being pressured by others’ expectations.
And also “I believe in you,” “Aim high,” “I trust in you” are a similar thing, and it’s not like external opinions even matter anyway. Intrinsic motivation is far more powerful...!

Thus

Can does not imply will. Improvement is not guaranteed! As with many things in life trying to say something positive to a person feeling negative might be socially accepted but not for the person who is feeling negative!

Category:Logic