In ExtremeProgramming terms, it means to work at a SustainablePace. Generally, although not always, you shouldn't work more than a FortyHourWeek.

''Please note that this only applies to full time, salaried people. Contractors, consultants, and others working on an hourly basis are often willing to put in whatever amount of time the client wishes to pay for, particularly if there is no other work in house at the job shop.''