I got very lucky -- I was in the right place at the right time.
I was a worker bee (engineer, senior, but no direct reports) at a BigCo. Soon after I started, the stock went up and kept going up, beyond anyones' imaginations. After seven years, a few thousand options (plus more approximately-annual options grants) turned into a couple million before taxes. I held on to them as long as I could -- exercised and sold half immediately after quitting, and the other half for 90 days later.
It was a wild ride but I'm really happy to be more diversified now! Besides, the golden handcuffs were starting to chafe and I was seriously burned out; the money definitely kept me there longer than I otherwise would have stayed. No regrets though.