I quit the Napali trail at the helicopter landing zone
You can tell this whole hike through three signs.
The first one tells you where you are

Napali Coast State Wilderness Park. Wilderness is doing real work in that sentence and I did not give it enough credit.
Most people call this the Napali trail. Its actual name is the Kalalau, and the first stretch of it runs out to a beach two miles along the coast.
The second one tells you how far you have come
A quarter mile. The markers out there are small, and this is the whole of one.

It is sitting in the bottom of this next one, if you know to look for it.

A quarter mile in and you are already looking down at the water like that. This is the part everybody photographs, and it is genuinely that good.
Look at the rock on the right of that picture. It is wet. Everything up there was wet.
The mud
The dirt on Kauai is red and it is slick. Not slippery the way a wet sidewalk is slippery. Slick like someone greased it.
I went down early, on a downhill going into a curve. Not a stumble. Down.
There are no guardrails out there. No fence, no railing, nothing on the outside edge of the trail, and in places it is a sheer drop. Which way you fall is not really up to you. I was lucky.
I got up and kept hiking, around the curve and along the coast, and it opened out to this.

The third sign tells you something else
The curve came back around, and this is what was waiting at the end of it.

Helicopter landing zone. Stay clear at all times. One and a half miles.
That is what a landing zone on a hiking trail is for. People get hurt out here, and there is no road and no way to carry somebody out, so a helicopter comes and lifts them off.
I had already fallen once. I stood there reading it, in the same red mud, and said I was done.
If you go
Go. The quarter mile marker alone is worth the drive, and you can turn around anywhere you like. Nobody is grading you.
Just know what it actually is before you start. It is not a walk to a viewpoint. It is a wilderness trail with no guardrails and a drop on one side, and when the mud is wet it decides how far you get more than your legs do.
Turning around early is not failing at it. That is what the markers are for.