Obviously, nothing is ever completely wasted because it’s all a learning moment. You can learn from anything. But for example, when you go back to school, 99 percent of the term papers you did, books you read, exercises you did, things you learned, they don’t really apply. You might have read geography and history you never reuse. You might have studied a language you don’t speak anymore. You might have studied a branch of mathematics you completely forgot.
99% of effort is wasted