There is no such thing as perfect practice, because humans are imperfect. There is no such thing as perfect mindset, because humans are imperfect.
Practice does not make perfect. Practice makes permanent. Yes, we should be striving for perfection – but we should also recognize that perfection will always be beyond our reach. When we practice, we should first learn the best ways to do things. This means learning from others, not simply from our own ideas of how things "ought" to be.
There is nothing wrong with reinventing the wheel. However, when we do so, we should be sure that we are not trying to drive on trapezoidal wheels with offset axles.
Also, just in case my earlier post was unclear: of course you aim for the upper center chest when possible. That is where the good stuff is, such as the largest blood vessels in the human body, the heart, and other vital organs. The goal is to shut down the attacker as quickly as possible, and exsanguination is as good a way to do that as any other. However, it is incorrect to say that a shot or two to the chest "usually" ends in death. The facts are simply otherwise, as those who work the emergency room in any trauma center could tell you.
My personal website: Cornered Cat