What return actually means
Return sounds like homecoming. Something restored, something arriving back where it belongs. That is not what 反 (Fǎn) describes. 反 is the moment a thing stops going one way and starts going the other. Not the destination. The turn itself.
Chapter 40 of the Tao Te Ching is one of the shortest in the book, and it opens with four characters: 反者道之動. Reversal is the movement of the Tao. Not reversal as a setback or an interruption. Reversal as the actual mechanism. The way things move is that they go out, reach a limit, and turn.
The tide shows it plainly. At the lowest ebb the water is not repaired or rescued. Nothing intervenes. The sea simply stops withdrawing and begins to come back, because reversal was built into the movement from the start. The same is true at high water, where the turn is equally certain and considerably less welcome.
This is what makes 反 uncomfortable as well as consoling. It is one law, and it reads two ways depending only on where you are standing. Near the bottom, reversal is the thing coming to get you. Near the top, it is the thing coming for you. 反 does not take sides, which is exactly why it can be trusted.
Where Lao Tzu speaks of it
The cost of assuming a line
Modern life is arranged around the assumption of a line. Growth continues, careers ascend, metrics go up and to the right. When something declines, we treat it as a malfunction to be diagnosed rather than a phase of a movement.
The cost lands in both directions. On the way down, a hard stretch feels permanent, because a line has no turn in it, so the bad period is read as the new baseline rather than a position on an arc. On the way up, the same assumption makes success brittle, since a thing believed to only continue is a thing you never prepare to hold differently.
反 offers a shape instead of a line. It is worth being precise about what that does and does not claim. It says that things turn, that no direction runs forever, and that this is a property of how movement works. It does not say that your hard thing is secretly good, that it is happening for a reason, that it will resolve on any schedule, or that what returns will be better than what left. The pattern is real. The promise is not on offer, and a principle that also predicts the end of your good stretch is clearly not a comfort blanket.
Think of one thing in your life that currently feels fixed, good or bad. Ask where on its arc it might actually be. Not when it will turn, and not into what. Only whether you have been reading a position as a permanent state.