If you succeeded every time, be it in practice or competition, you would have to start asking yourself whether the challenges and goals you are setting forth are appropriate.
You are not supposed to succeed in every training session or every race.
Success is necessary for many reasons but it should not be expected on every outing. What should be expected is a best effort and a commitment to the task presented in that moment. What should be expected is a commitment to the process regardless of the outcome.
If you succeed in every aspect of every training session it may indicate that you are not pushing the boundaries of your own capability. Such an approach leads to stagnation and complacency. There should be some training sessions, sets, or situations that are perhaps just a fraction out of reach. There should be some training sessions and racing situations that come with an uncertainty as to the outcome.
Success is necessary with frequency because success is fun and success is motivating and success indicates that the effort being put in is working but it should not be expected every time.
Success in every aspect of every training session may mean you are failing in the big picture. Failure on occasion probably means you are succeeding in the big picture.