Firing one person in a 10 person company could mean that you lose your entire accounting/finance skillset in one fell swoop. Or your sole developer. It is a big deal in terms of intellectual property and skill pool within your organisation.

Down stream impact of how to cope with that loss is another factor. Fire your book keeper and does your remaining engineering team have to spend 10% of their time doing invoices and reconciling bank accounts?

Pretty much, yeah. In an 11 person company, each individual is basically a whole department. That one person might be your only marketer, or your only frontend developer, or your only accountant. That's a really big deal.

To be fair, a firing in an 11-man company can be a pretty big deal.