In the high middle ages, both kings and lords maintained military households of varying size. At any given time, there would be household knights and soldiers hanging around. So, while any great man would have armed men around him at almost all times, they weren't dedicated guards. Like, if you were part of a lord's military household, you probably didn't have a regular shift standing guard by a door. You did what was needed when it was needed, as directed by the lord or his marshal. You might be keeping watch one day, or riding a patrol the next, or just hanging around the great hall.