[cutemonster]

What about this way of looking at the it's-possible scenario:

That means there's a way for the cannot-do person to actually do it, s/he just needs to figure out how, maybe with help from others

Good news?

And there's no need to blame him/her -- not any more than someone who got a cold which can happen to everyone

I wonder what caused you to thinking in terms of blame and lying

(The other scenario -- when the can-do person in fact did sth else and says it's simple -- can be annoying indeed)