One of my first boss called it the bus factor, not sure where the term comes from. What's the minimum number that need to get hit by a bus before it's impossible to keep things running. He used to say "you always have some bus factor, but it should never be one unless you're alone, otherwise you deserve whatever crap is going to rain on you someday".
I've found that to be incredibly true in my career.
I've found that to be incredibly true in my career.