This depends very much on context.
If the person were making boasts or threats, then the term paper tiger would fill your first space well. I don't think there's a single word which would fill the second as comfortably.
I'm going to assume from the Russian word you provided, though, that you mean something like they assumed (or acted as though) it were unnecessary to follow through, in which case I can think of several pairs that might work for you:
- … very lazy and pure laziness [lack of motivation]
- … [no very] rather effete and passivity [lack of … something¹]
- inconsistent and inconsistency [flakiness, lack of commitment]
Finally, @Michael_B has already suggested unreliable for the first position; I'd suggest spelling out the second as A lack of reliability but that's a personal style choice, not a hard-and-fast “grammar rule”.
¹ There are a lot of somethings that would fit here: strength, forcefulness, decisiveness, …