Working harder is not our default position

Our default position is not to work particularly hard. Farming societies overcame this default with cultural exhortations to work harder and social norms about when to work and rest. Also, the relative poverty of pre-industrial people ensured an incentive to work hard. If you didn't, you had nothing to eat.

In our more recent affluence, we tend to work less intensively than we should, even if we could reap more rewards for hard work.