The push-up plank is a ‘pose of reflection’.
In order to hold it for 3, 4, 5 or more minutes – with good form – you must look deeply into your own mind.
If you’re afraid to do that, you will fall down.
You must be with your thoughts.
You must breathe.
You must allow whatever comes up to do so without attempting to suppress it.
When you do this, you train your mind, and change your body.
As Joseph Campbell said, “The cave you fear to enter holds the treasure you seek the most.”