My answer to a Quora question:
History is a useful narrative constructed from what we know about the past. Let me unpack that bit by bit.
"History is a ... narrative..." History is not an accurate reproduction of the past and it is not all of the facts. History is a story (as the word indicates). We know he names and home towns all of the soldiers involved in D-Day. We know what many of them ate that day. We know the technical specs of their weapons, who designed, and who manufactured them. We know the logistics of getting them to the beach, the support efforts, and the casualties. To wrote a history of that day, the historian has to pick and choose through all of the raw data--the facts--to decide what is necessary to tell the story they want to tell.
"History is ... useful..." No historian is completely random in picking their narrative. Again, look at military history. A narrative based on the same data/facts might describe a glorious victory, a unredeemed tragedy, or illustrate some aspect of the human condition. Facts and interpretation are two different things. This is why conservatives get so upset about how history is taught in the schools. Each new generation of historians reinterprets the same facts in the light of their experiences. Conservatives want history to be carved in stone. Facts are facts. History isn't facts; history is interpretation of facts.
"History is ... constructed from what we know..." We can't know everything. This is obvious in the far past where we take every tiny data point and try to squeeze as much information as we can from it. Every decade or so we have an earthshaking discovery in ancient history. Here is a city that dominated this trade route for three centuries and this changes everything we thought we knew about the cities on either end of that trade route. Even in something as information rich as the D-Day example, there is an enormous amount we don't know. What were the conversations that led to important decisions. Who knew what and when did they now it.
It's an historian's cliche to refer to history as a jigsaw puzzle with missing pieces, and no box to show us what the picture should look like, and no edge pieces, and a few handfuls of pieces from other puzzles added, and a hyperactive cat in the house, and half the pieces are wet... and that's why we love it.