if you don't know ahead of time every reaction to every scenario then don't even start - but some like myself had to learn by losing so don't know if it's possible to get the lazy mind to be desperate without actually being in a critical dilemma.
I think that's the case with everyone @MarkBrown Experiences make us learn better, for so many traders losses play a turning point in their trading journey. And so I think every trader should give it a try, no matter he incurs a loss. What's important is how he analyses that mistake and learns from it.