A threshold is commonly defined as:
1. a strip of material that separates two rooms or the outside from the
inside of a house
2. a runway
3. the intensity that must be exceeded for a transformative
4. a level at which something new kicks in

All of these are about moving from one frame of reference to another.
If we look beneath the surface we see that a threshold is the gateway
into another world. Most often when we feel we have reached our max, or
are overloaded, it is an indicator that we are about to hit a new level
of performance.

It can feel scary or overwhelming just before we hit our stride and
enter a new dimension.  Often the very act of giving up in the
face of extraordinary demand is exactly what it takes to reorient
around a new organizing principle, which makes it possible to reach a
new, unprecedented intensity.

Where are you being called to hit a new cadence, one that is above and
beyond your previous best?

The teacher who is
indeed wise does not bid you to enter the house of his wisdom but
rather leads you to the threshold of your mind.

– Khalil Gibran