Is it not about having the skills and experience to get by everywhere in a stack? So if someone is missing, you are able to pick it up, even if you usually don'

Is it not about having the skills and experience to get by everywhere in a stack? So if someone is missing, you are able to pick it up, even if you usually don't work with that part? Rather than say "that is a backend job, I am frontend". Perhaps usually you work frontend, but once in a while, something needs fixing in the backend and you are the best one to do it, due to sick leave, deadline crunch or whatever...