The more rare you are, the more you are valued. You still have to be useful to be valuable though.
In order to acquire those rare skills, an ungodly amount of work is often required. It is also a huge variable. A rare skill today can become useless tomorrow.
Also, beware of indispensable people. "This company needs me" can have all sorts of causes. Maybe you didn't documented things right, maybe you just have a long history with them. It doesn't mean being rare. Being rare is feeling "this skill I have could be of use to any similar company and few people know it".
The skill could be anything. Perfect pitch, excelent document writing, de-escalation, low-level bit shaving.
I'll add one more to this, "Pleasant personality". If you have are difficult to be with, you will be miserable and so will others around you, leaving you with very little or no allies. So new formula:
Valued = Useful + hard to find + easy to work with
"Easy to work with" is a wide requirement. It's harder to find.
But we can compare how far "easy to work with" goes in a more balanced scenario:
You're hiring for a critical rare skill. _Only two_ candidates were seriously considered, and you hired them both.
One of them delivers for the skill you hired (useful), but is not easy to work with.
One of them does not deliver for the skill you hired (useless), but is easy to work with.
So, it doesn't matter what your definition of "easy to work with" is in this scenario. It justs matters that whatever it is, it's not related to usefulness (so you can't get away with "but being useful makes you easy to work with").
Who would you lay off if your bills were depending on those guys?
The more rare you are, the more you are valued. You still have to be useful to be valuable though.
In order to acquire those rare skills, an ungodly amount of work is often required. It is also a huge variable. A rare skill today can become useless tomorrow.
Also, beware of indispensable people. "This company needs me" can have all sorts of causes. Maybe you didn't documented things right, maybe you just have a long history with them. It doesn't mean being rare. Being rare is feeling "this skill I have could be of use to any similar company and few people know it".
The skill could be anything. Perfect pitch, excelent document writing, de-escalation, low-level bit shaving.