These days, when we call something a “myth” we usually mean it’s a “lie.”

But the word also has a more important meaning: A myth is a story that gets passed down in a culture over generations that explains how the world works. Historical accuracy is less important than what the story says about people who pass it on.

The story of the Pilgrims and the first Thanksgiving is based on historical events, but it is also a myth.

It goes like this: Seeking religious freedom, Pilgrims crossed the Atlantic Ocean and landed at Plymouth Rock on Nov. 11, 1620. Before going ashore, they signed the Mayflower Compact, a mutual agreement that the community would stick together, write their own laws and live by them, creating the first system of self-government in the new world.

The first winter was harsh, and half the colonists died. But the next spring, their Indian neighbors taught them how to hunt and plant crops. To celebrate their first harvest, the Pilgrims held a feast of Thanksgiving, inviting their Indian friends, beginning a tradition that we continue today.

But here are some of facts that usually get left out of the story: The Mayflower left Holland at the wrong time of year, headed for land at the mouth of the Hudson River, near what later became New York City, but was then considered part of the Virginia colony.

About half the passengers were religious separatists, who had no interest in freedom of religion for anyone other than themselves. They modestly called themselves “saints,” not “Pilgrims.” The rest, who they called “strangers,” had less spiritual reasons to escape life in England, some looking for commercial opportunity, some trying to stay out of jail.

After two months at sea, blown off course by storms, the Mayflower laid anchor about 200 miles northeast of their destination. Exhausted from their journey and nearly out of beer (the only beverage thought safe to drink, even for children) the Pilgrims and their hangers on wanted off the ship.

Some of the Strangers argued that since they were not in Virginia, they did not need to abide by the contract that they’d signed with the colonial authorities. The Mayflower Compact was the hastily drafted agreement to end the mutiny.

It’s true that half the colonists died the first winter, and that there was a good harvest the next summer. There are reports of a harvest celebration, which the Pilgrims probably wouldn’t have called “Thanksgiving” because that had a technical meaning in their religious practice, and it happened in September, not November. There are reports that Indians were present, but no contemporary account says they were invited.

It’s in its telling of the role of the Indian neighbors in which the story peels off from history.

When the Mayflower arrived, the Massasoit had recently lost 50 percent to 90 percent of their population to plague, probably introduced by European fishermen. The Plymouth Colony was founded on what turned out to be a graveyard, a former Indian village that had been wiped out by disease, something that the newcomers took to be a sign of divine providence. The local tribe had an interest in helping the newcomers — the two communities needed each other. But together they also engaged in combat with other local tribes over territory.

And it’s a good thing that the official story ends where it does, because what happened next does not create a warm holiday feeling. What followed was a centuries-long process of conquest, as European settlers and their descendants claimed the continent for themselves. The homey scene of Indians and Pilgrims at the first Thanksgiving blots out much more horrifying images of war and extermination.

The story of the First Thanksgiving that we grew up with is based on history, but enough details have been left out or invented to make the whole tale something other than the truth.

But it’s not a lie, either. It’s a story about bravery, sacrifice, cooperation, and inclusiveness. It’s a story about throwing off the shackles of an old world and building a new one where everyone has a place. The values that were later attached to the Mayflower Compact and the First Thanksgiving are values that still inspire us.

It’s a story about who we want to be, not necessarily who always are — which makes it an important founding myth, and makes it something worth celebrating.