Improvisation is like surfing. You don’t know what waves you will find, you just start playing and see what happens. The course of the waves are like the course of an improvisation. The improviser must keep balance and respond to the shifts in the music. Sometimes there are wipeouts, like at the end of this one.
One of the nice things about improvisation is that each piece is ephemeral. Rarely ever can an improvisation be repeated and work. Once it exists, a second version will likely be contrived and not interesting.