The story behind the design
There is no up. Try remembering that in the dark.
Darkness and blindness do interesting things to the mind. Add a rock ceiling and no direct route to the surface, and even the calmest diver may discover an entirely new personality. The cave is not interested in meeting it.
Tying a line around a tree while blindfolded can be a useful drill. If a centre treats that as proof you are ready for a flooded cave, untie yourself and leave. Preferably before they congratulate you again.
In Asia, we recommend Mikko Paasi and Koh Tao Divers, together with Claus Rasmussen of Tech Dive Asia. We will not retell the Thai and Laos cave rescues here. The internet already has enough coverage, interviews and dramatic YouTube thumbnails. Read them and decide for yourself what real experience looks like.
Then read Jill Heinerth's Into the Planet. She writes about recovering a fallen friend from inside a cave. If that does not make you treat cave diving seriously, this shirt cannot help you.
For those heading towards Mexico's cenotes, DarkSide Divers also comes highly recommended. Beautiful water, extraordinary caves and absolutely no exemption from being properly trained.
The skull is not there to make cave diving look fearless. The diver inside it follows a continuous line because bravery is less useful when nobody knows the way home.
Respect the ceiling. Protect the line. Keep your imagination under control.
Diving involves risk. Read the disclaimer.