And at small companies, a boss may fire someone they just don't like personally. And not all bosses at small companies necessarily understand what their underlings do for a company.

At big companies, if it is done right, the upper level management may ask for input from 1st line managers as to who they should fire. Also, my last company, all managers had to rank their underlings, and those at the bottom had a chance of being trimmed if there were layoffs.

Many big companies will listen to those first line managers, and almost any upper-level manager is aware of their lack of knowledge about the leaves of the management tree.