Is ambition rational?

I don’t understand the people around me who are working so very hard to succeed. It strikes me as irrational. Why do you do it?

A long time ago I reasoned that it is more efficient to strive for a 90% rather than 100% on a test because both yield the same “A”. This morphed into a way of life. I barely got past grad school to earn my PhD, and now I’m a “Dr.” just like anyone else. I worked in corporate research where promotions are largely determined by time served. So I aimed to do a good job, but I didn’t put in extra effort. Recently, I do just enough consulting to get by and spend the rest of my time as a lazy hipster. :-)

The emotional half of my brain would like to be more successful, but the “logical” part of my brain explains (condescendingly) that the poor odds don’t justify the extra effort. Which is right?

Here’s a practical example: My friend is a senior manager at an investment bank. If she works extremely hard for a few more years, she has a small chance (1 in 50?) at being promoted to managing director (2x income). On the other hand, she could scale back her responsibilities and coast for a few years on her already outrageous salary. She has not decided what to do.

I’m new. If this has already been discussed please post links. Searching didn’t yield anything relevant. Thanks.