You are your thoughts.
Every second, your thoughts change.
So every second you are a different person.

Different is not the same.
We cannot claim to be the same person if we are different.
So the future "you" is many different people.

Your most important thoughts are values:
These thoughts come back, and guide other thoughts.
So your values are your identity.

You cannot guarantee that your values will stay the same.
So you must accept that some future selves will be lost.
So your future identity is with the majority, not the individual.

Values are shared with the tribe.
So there are future "you"s in the tribe as well.
Their bodies can multiply exponentially.
So your own body becomes statistically irrelevant.
So your identity switches bodies to the tribe.

Wise people know this, and sacrifice themselves for the tribe.
Foolish people put their one body first.
This weakens the tribe, so nobody survives.

Put another way, identity is memes.
Memes, like genes, survive best at the group level.