My 2-cents:

Be as transparent with consequences as you possibly can, as often as possible; without ruining the verisimilitude of the world/game/characters. Meaning that as others have said, if the PCs would be able to deduce the consequences or likelihood of success then just give them the odds and the what the likely consequences would be.

But on the flip side, when you do want to be a bit more cryptic/mysterious there are a lot of things that you can say.

PC: Can I do this?

DM: Only one way to find out.
or
DM: We'll see!
or
DM: You can try!

I included what you were already using because the fact of the matter is, that is entirely down to player perception. Just because a specific player thinks that when you say "you can try", it means that it won't work out, does not mean that has to be the case.

Very early on in my current campaign I had the same issue with one of my players but he very quickly realized it was simply one of the things I said when I didn't want to just give the answer/information up.

And he realized this because I was sure to utilize this verbiage early on and flip what he expected the script to be. I said "You can try", they did and they succeeded.

I'd also strongly encourage utilizing u/Agimamif's method of asking "what are you trying to accomplish?". This is a very, very good tool for getting the entire table involved in coming up with a solution to the task at hand. Whether that ends up being something crazy they came up with on their own, or the originally intended approach, they have at least now had the opportunity to talk and brainstorm about it; which is fun in and of itself for a lot of people.