As a former government employee, a year is plenty of time to evaluate. There are clauses in the rules that allow firing after that time (morality clause, violation of security clearances, etc.), so it is not impossible to get an incompetent employee out-I have seen it happen. However, because there is a hearing process, people do have the mistaken impression that it is impossible to fire a government employee. There are plenty of ways (R.I.F.s), but I do think if an employee is not going to be competent, it is very hard to hold up for an entire year to "fool the system".