6 out 7 start ups I worked for never had a liquidation event that resulted in any monetary gain.
The one that did ( i was employee #97 and worked there for almost 6 years) and they finally had a 2ndary offer which allowed me to sell 15% of my shares, for about 7K, but because it's short term gains, about 4K is what I got after taxes.
The rest of the shares were completely worthless because they couldn't be sold. I am not disappointed. I never assumed the options would ever be worth anything - I choose my employment based on Salary and work life balance. Options are just a nice bonus, if they do happen.