An employee’s attempt to become “indispensable” can create a toxic work environment, if they’re insecure or ego-driven.

One can just watch and let a colleague spend days or weeks learning something esoteric, when one already learned it (on the company’s time) but keep tight-lipped as if it were one’s own intellectual property.

Or the programmer who writes a piece of code that is so complicated, that nobody else can read it let alone modify it without breaking something. And sometimes they treat it like a badge of honour, as if it exemplifies their seniority and brilliance. It’s a bottleneck and a liability.

Of course there are positive ways to become indispensable but not everyone can be, so if everyone were pressured to try, you’d get a mix of good and bad but probably mostly bad.