When learning a new technique, judo practice begins by thinking through the mechanics of a technique and then repeating the movements, by the numbers, multiple times. This then evolves into hundreds of uchi-komi and nage-komi. But true success in judo is seen when that new technique comes reflexively in randori, executed without thinking. Randori, against an unwilling partner, is the true validation of all that training and repetition. To be successful in randori, or shiai (competition), throws, counters, and combinations must be pre-programmed into the neuro-muscle memory, where they can be triggered by the movements, actions, or reactions of your opponent. The perfect Ippon is often executed reflexively, surprising both Uke and Tori.
Mark Lonsdale, Judo Training Development