Are weak people intrinsically immoral?

It seems like sometimes there are people who just fuck over absolutely everyone around them, but they always claim they are doing it because of some external factor i.e. someone else was putting pressure on them or they didn’t have the funds or anything else they claim is out of their control.

Are people like this just weak or are they just total manipulative liars? If it is weakness and these people are just too buffetted by events, does this mean that weak people are, by their nature, immoral and incapable of keeping a promise?