Beyond a certain minimum absolute, the most important point of is one’s perception of _relative_ performance. This comes into play in many ways.
For instance, 20 miles on a bicycle in 90F may seem like a deathride. Yet this is only the case if 20 miles or 90F is the limit of peak performance. If peak performance is 100 miles and 105F, then 20 miles and 90F will be easy enough to repeat daily.
I believe it was mentioned somewhere that most mammals are alloted about (which a factor few) 1 billion heartbeats (that would make a human live 35 years which is a typical age in nature). A person in fine aerobic shape will have a resting heartbeat rate of less than 50. For that person a stroll will barely get the heartbeat up to 85 which leaves plenty of room for jumping, talking, and fooling around. A sedentary, aerobically speaking, person will have a normal heartbeat of 75—individuals may differ—and thus a stroll will drive the heartbeat up over a 100 which will be felt as exertion and so there will only be room for walking with no energy to spend. If we really do have about a billion heart beats before the heart wears out—of course it’s not exactly 1,000,000,000 for all of us, some have more, some maybe less—this also means that a lower heart rate lets one live longer or more accurately, live better for a longer time. Early retirement has also been shown to increase lifespan.
The same goes for space. Space that is 75% filled seems large. Stuff can easily be stored and moved around. Space that is 100% filled seems small and stuffy. This is the key to living in small spaces. Just have less stuff. Keep the ratio, not the stuff. What normally happens unthinkingly is that one start with small living quarters, say 100 units of storage at 75%, that is, filled with 75 units of stuff. Then stuff creeps in until there are 100 units of stuff for 100 units of space. The space is then “upgraded” (while discipline is downgraded) to 133 units and the 75% comfort level is restored. Once again stuff creeps in.
This is why I like my shelves partially empty and why I prefer being somewhat “better” than necessary for everything I do. This allows me to enjoy things much more than being stressed at the limit.