Don't be the first employee when you're being hired by one person and they've already built most of the product. You'll be treated as a "do this, do that" mule. Where you should be treated as not a cofounder, but at least an important partner, this does not often happen.
Is there ever a point where a single person has "built most of the product"? At that stage, the product has so much evolution left, that early employees are going to be critical to shaping and developing it.
It's almost certainly a matter of viewpoint and attitude of both the founder(s) and early employees though, so discretion is required.
That depends on the founder. In the 90s I was the first employee of a startup. The founder (now a prominent investor) treated me like an important partner. Fifteen years later we're still friends and do business together.
When you say "this does not often happen?" how many instances do you know?
Sure, but I think you can agree that's one of the worst scenarios - there might be slightly better ones (softer landing, taking money off the table, etc.), and some worse (legal troubles, decades-long debt, broken relationships), but this is a common "worst case."
