Why are you an MD / why become an MD?

Despite the demographic of this site, I've always been curious as to what the motivation is behind becoming or being a Managing Director in IB?

Is it because you love IB and wanted to be an MD from day one? Is it because you want to be the next big rainmaker? Perhaps you want to one day launch your own advisory shop one day? Is it because you didn't / couldn't go to the buy side? Do you love meeting industry / business leaders? Or because you're tied down due to family, mortgage etc.?

I'm not trying to put anyone down or take away from anyone's accomplishments about becoming or being an MD. In my opinion it's impressive that someone makes it to MD, but I do want to just understand the mindset behind the career decision a little better (as I'm just curious like that). Would appreciate all seniors sharing their insights / perspective, as well as anyone who can share the perspective of MD's they know themselves.