Burn not your candle at both ends at once.

A candle lit at both ends is used up unusually fast. The image warns that energy and other limited resources can be depleted by trying to sustain too much at once.

The advice is to pace one's efforts so that present demands do not leave too little for what follows. It calls for restraint, not for avoiding hard work altogether.

Use it to caution someone whose simultaneous commitments or intense pace may be hard to sustain. It works best as advice to conserve energy or time, rather than as a criticism of ambition itself.