Both have their own pros and cons. When you succeed you feel confident and also determined to succeed in the other tasks as well. When you loose you break down completely which makes you question yourself and your potential, sometimes even your existence. This makes you rise again and you now are well aware of your strengths as well as your weaknesses.
Hence the biggest teacher is life and you learn better when you live that life in real means.
And also the meaning of living is different for everyone, so as long as you fall down and are still determined to get up and keep moving, it means you are living and you have learnt your lesson.