Well....
There are a few uncomfortable things we do in flying that teach.
For example, the cross-control stall demonstration isn't comfortable for most students, but it teaches "this is not good and I don't want to do this so I will avoid doing that." (Some will love it and you just shove them over to the local aerobatics instructor).
So is the power-on stall with little or no left-turning tendency correction (also usually results in a spin).
So is flying into clouds.
(Off thread Aside BEGIN)
My intent is to not send a PP candidate on to the practical until I've taken him up at least once in actual so he/she can feel the disorientation and think "I didn't like that feeling -- I'm going to avoid that until I know how to fly on instruments."
I think FAR too many students these days have spent time in front a of a flight sim where the panel is primary and figure "I fly 'on instruments' all the time-- it's no big deal..." These need to experience flight in the clouds before they will believe that they will lose control.
(Off thread Aside END)
Pain inflicted by shackles and pungee sticks has no place in flight training, of course (unless you're going after a very niche market).
Flight training is all about expanding envelopes. The good teacher knows when the student is ready to push out that edge a bit more, and when it's at the limit.