Ambition starts turning into greed when nobody else at the table gets fed.

The useful line is not about how much you want, it is about whether anybody else benefits. Wanting a lot is fine when your getting more means the people around you do better too. It becomes something else when the arrangement only works if they get less, which is a structural test rather than a feeling, and therefore easier to apply honestly. Ambition is decent company; greed is one particular shape of it.

Look at the arrangements you are in and ask who else comes out ahead. On a group project, a shift, a team, check that your gain is not coming entirely out of somebody else’s share.