Sadly, examples from the dotcom burst and housing crisis abound. It's a double edged sword. I have always preferred to go for early exercising.
"Many of these workers now owe far more in taxes than their stock is worth. Former Cisco engineer Jeffrey Chou, 32, owes $2.5 million in taxes on company stock he purchased last year that has since withered in value. Chou figures that if he were to sell everything he owns, including the three-bedroom Foster City, Calif., townhouse that he shares with his wife and 8-month-old daughter, the family still could not pay the bill."
"Many of these workers now owe far more in taxes than their stock is worth. Former Cisco engineer Jeffrey Chou, 32, owes $2.5 million in taxes on company stock he purchased last year that has since withered in value. Chou figures that if he were to sell everything he owns, including the three-bedroom Foster City, Calif., townhouse that he shares with his wife and 8-month-old daughter, the family still could not pay the bill."
* https://www.chicagotribune.com/sns-tech-taxes-story.html