I think there's a difference between practicing struggle and practicing under stress. I see practicing struggle as reinforcing what someone knows is wrong; which they'd do because they believe they only need to improve their fitness to get faster.
Practicing under stress on the other hand would be trying to maintain technique when you can feel your form breaking down due to fatigue or some other factor.
Here's the good stuff:
So far my focus had been on numbers - how many strokes it was taking to complete each lap - and technique thoughts. Now I gave myself over to creating a "cocoon" within which I felt only ease and relaxation. Relaxation in my stroke, my breathing, my turns and pushoffs, my rhythm. Countless times, the pain in my stomach, the burning in my lungs, the heaviness in my limbs would poke through my consciousness. As soon as I was aware my focus had gone there, I'd redouble my attention to feeling relaxed.
If TV has taught me anything, it's that you can only attain a state of grace when it feels like you have a good chance of failing. So if you look for, and embrace those moments in training when you're faced with failure, they should be easier to handle when the cameras are rolling.