In 1954, Roger Bannister was the first man to run a sub-4-minute mile. Within 3 years, 16 other runners had also. The psychological barrier had been broken.
The one arm handstand pushup holds a similar mystique. While some say it is impossible, others are busy training for it.
I've been working my one arm handstand a lot, and my pressing strength is the best it has been. Here now is some work with the assisted one arm handstand pushup. I'll say I prefer the 2-3 finger assist the best.