They don't fire for every mistake.
Many employees fear that they will be set adrift in the wake of a reasonable decision that didn’t work out, or after a minor blunder. They worry that for all of the talk about loyalty, if loyalty becomes inconvenient, management will not support them. Vague standards and arbitrary enforcement of rules foster that fear. Employees gain confidence when they know where the swamps are and how to avoid them.
See more on managing errors.