What does "burning the candle at both ends" mean? [closed]

It has two meanings.

If you got a candle, and somehow fixed it to something in the middle, then you could quite literally light both ends.

While producing slightly more light, this would waste your candle by using it twice as fast. This is the only meaning the OED gives, with the first citation being from the 1736 Dictionarium Britannicum:

The Candle burns at both Ends. Said when Husband and Wife are both Spendthrifts.

Another sense sometimes used is that if one is working particularly long hours, then one must light a candle at one end of the day, as one starts in the dark of the morning, and at the other, as one ends in the dark of the evening.

This sense though is perhaps a folk-etymology of what was originally meant by saying that such a person is being wasteful—hence the first sense—of "life's candle", however they may perhaps be otherwise thrifty.

burn the candle at both ends is an idiom meaning to exhaust oneself, esp by being up late and getting up early to work; to work extremely or excessively hard; to work too hard for good health or peace of mind. Worsened by also "partying hard" on top of working hard (but not a necessary component to the definition).

A candle lit at both ends will burn up more than twice as quickly/last less than half as long as one lit on one end alone.

From www.phrases.org.uk

it was first coined in the 1700s. The 'both ends' then weren't the ends of the day but were a literal reference to the two ends of a candle. Candles were useful and valuable and the notion of waste suggested by lighting both ends at once implied reckless waste. This thought may well have been accentuated by the fact that candles may only be lit at both ends when held horizontally, which would cause them to drip and burn out quickly.

Nathan Bailey defined the term in his Dictionarium Britannicum, 1730, by which time the phrase had already been given a figurative interpretation and the both ends were a husband and wife:

The Candle burns at both Ends. Said when Husband and Wife are both Spendthrifts.

Randle Cotgrave recorded it in A Dictionarie of the French and English Tongues, 1611:

Brusler la chandelle par les deux bouts. [To burn the candle by the two ends]

Edna St. Vincent Milay had a different take on living to the fullest/living "hard"

from Figs and Thistles: First Fig By Edna St. Vincent Millay

My candle burns at both ends;
It will not last the night;
But ah, my foes, and oh, my friends—
It gives a lovely light!