In us older men, it appears that prostate enlargement prevents fully
emptying the bladder
when one micturates.  At least, so I have read.

My personal experience is that I cannot go too long without peeing. Maybe
two hours.
Then if I don't go, I may suddenly have to go, and can hardly reach the
toilet without
some spurting.  Exactly why is this?  Is it that the bladder is suddenly
totally full?
Why cannot I notice it gradually?  Can someone explain this?

I think there is a mental effect too.  When I realize I must go, I must go
NOW!