Is the lack of ambition due to lack of ability, or lack of motivation?

Sometimes I think to myself, if right now I had more responsibilities, would I have the same lack of ambition? And the answer is a straightforward, outright no.

What if today we have people to take care of, people who is completely dependent on us whether it be in work, family or friends. How then can we justify the same actions right now that we are doing?

And therefore, how can we justify what we're doing right now, in this point of our life, if we know all along, its because we can afford to, and not because we should?