I was the third employee at a startup. I was young and stupid and thought "20,000 shares" was a lot. I worked my ass off, it was immensely stressful, but we built and launched a product. I later found out it wasn't much of a stake at all- .1% and that's even before any dilution shenanigans and all that. We took a paycut part of the way through, had our 401k contributions slashed and such.
A company in the space (but doing something different) called and made me an offer for twice what I was making. I was the lead developer by that point, had my hands in every significant piece of code, understood how everything fit together and such, and was appalled when I found out that I had such a small piece of the total pie. I demanded more, like 20x more, and they made it sound like I was asking to sleep with their wives. Then they absolutely howled that I was screwing them over by leaving right at launch- they asked me to stay for 3 months, which I said sure- if you match my new salary plus a little more as a retention bonus and to make up for some of the paycut, and again they howled at how could I do this to them...
It was a painful lesson, but I learned something very important- Do not work like you are an owner if you are just an employee! I still to this day (this was 10 years ago now) feel very taken advantage of. I was working tons of late nights and weekends, was a super fanboy of the company, at one point I was going to buy us a company logo made out of Legos to hang on our wall, and now I just cringe at the thought.
There are so many ways to lose in the startup game, just so many, its really not worth playing anymore IMHO unless you are a founder or very early stage employee with material access to the financials and such.