The "bus factor" is a way of saying "how many devs could we lose on this project and still have a working knowledge of it?"

https://en.wikipedia.org/wiki/Bus_factor

A popular alternative I've heard here a few times is the "lottery factor".

How many devs could win the lottery and retire to a desert island while we still retain working knowledge of it.

Yeah but why shy away from the fact that any of us could randomly die at any moment? It may not be pleasant to think about, but it's true. And important to be plan for in critical systems.

That's a worse analogy. The entire point of "bus factor" is that it assumes the person is dead afterwards, so there's no way to recover the knowledge and this eventuality needs to be planned for beforehand.

Whereas even someone who won the lottery will take a $100k/hr consulting gig, or might take pity on his ex-coworkers and explain his choices in a 1 hour phonecall while sipping margaritas on the beach.

That way you don’t have to picture your team dead.

But it’s a reminder that they wouldn’t help if they had financial security.

That's much better - thanks.