During the bee keeping season (March to November) you need to do weekly inspections. The purpose of inspecting your hives is to keep them healthy and strong by heading off problems as early as possible before they become a big deal. And especially to avoid colony failures – dead outs.
Upon examination of a hive which has failed you might find that it is infested with hive beetle or wax moth larva, or that it is completely devoid of food stores. This might lead you to believe that those were the cause of the failure, but chances are that they were just the last of an unfortunate series of events which started much earlier – Which usually went undetected because the hive was not inspected regularly enough.