And that's why options are (mostly) a scam. If you leave before a liquidity event for any reason (they may not come, they take a long time, life circumstances, poor career growth, employers like to give shitty raises), you're stuck either investing often tens of thousands of dollars into an illiquid investment while paying taxes on it right now, or giving up your options. Sweet deal for employers either way. So when they hand out those option grants they probably get to apply a 50% discount or more to exercise.
Not to mention employers often try to avoid even telling employees what fraction of the total company their options represent, and definitely don't care to share their participation multiples. They're often very happy to let you think that in the case if a liquidation event, you get (exit amount) * (your ownership fraction) which just isn't true.
@apta: see [1] for a numerical example. You get taxed twice (or three times if someone is stupid) on typical ISOs:
1 - on grant, if the strike is less than the fmv (there are huge tax penalties for this, both for you and your employer, so it oughtn't happen)
2 - on exercise when you convert the option to a stock, on the spread between fmv and strike (but probably amt, depending on the type of option; it's mildly complicated)
3 - on sale of the stock, on the spread between the sale price and your basis
[1] https://news.ycombinator.com/item?id=7611512