If we only focus on making the best moves, we will never get the better of our opponent. When necessary, we must be willing to take big risks, and be prepared to lose everything. Unless we change how we fight, we cannot win.
If you begin to regret, you'll dull your future decisions and let others make your choices for you. All that's left for you then is to die. Nobody can foretell the outcome. Each decision you make holds meaning only by affecting your next decision.