We all like to see ourselves as the hero. We all like to imagine that in times of stress and danger we will rise to the occasion and take control of the situation. This isn’t just specific to self defense or competition - the happy escapism common to most people leads us to picture ourselves as smart, clever, skillful, entertaining and/or attractive in a whole variety of situations.
While mental rehearsal can certainly be helpful - especially when approached as a proper practice of visualisation - it can also give us the false impression that we can skip planning and preparation and happily handle the real situation should it occur.
What we forget is that outside of the fantasy we have imagined for ourselves, our body and mind is going to be subject to a massive variety of new stimuli - new sensations, emotions, fears, and automatic responses - that we can’t come close to imagining in the comfort of our couch. The result of all this extra chaos is that we are very likely going to make mistakes, be looser than we’d like, and skip minor details.
It is for this reason that our techniques should always have a high initial chance of success, and our defense always have a back-up. Even more importantly, the attention and dedication which we give to the quality of our performance within training should always be increasing; even as we get comfortable with increased pressure and challenge. An awesome technique will still be a good technique after the chaos of the real world is applied.
When we inevitably fall to the level of our training, we want that level to be high indeed.