“If you didn’t want to be understaffed when I called out, you should have hired more workers”

So I have a question regarding this concept that this group seems equipped to answer. The idea is that a workplace shouldn't be understaffed if a member calls in because the business should already have someone hired to take on the role while you're away. Does this mean the business should hire extra people that are only really necessary when people call in? Does that reduce hours for everyone because there are more people that need hours? Or is the idea that these workers are only coming in when you call in? I've been confused as to how it's supposed to work for a while so if someone could explain it to me I would be very grateful