In spite of Susan, seems you're hell for leather determined to set low levels on people's expectations. Albeit in the physical domain (actually it's more restrictive for reasons of actual capacity unlike mental activity)https://en.wikipedia.org/wiki/Four-minute_mile has something to say on the subject.
There is something to be said for realism.
The four minute mile didn't just topple for psychological reasons. It happened due to the development of better strategy (pacers), and continued to drop from there due to better training, better track materials, better shoes. The idea that it was purely a mental barrier is popular mythology.
