What a great feeling. With anticipation, you know the right things to do at the right times to correct a problem. Success becomes much easier to attain from acquired wisdom.
Think of a veteran mechanic. A wise craftsman will observe a problem for a short time and then know precisely what is required to correct it. From their experiential learning over time, they know with a high level of certainty what is wrong. No manual required, no computer testing equipment necessary, they have just come to know through focused learning experiences. To earn and possess the depth of a wise veteran is a great feeling, for both the mechanic and the consumer of their services.
Before wisdom can be attained on a particular matter, most of us will have to read through the manual first to discover the problem. Run the diagnostics with trial and error and more trial and error to learn the principles and the rules of the work needing to be done next. This often takes time, but you do so with a passion to become masterful in your work. The alternative is to just do your job without growing from the depth of your experiences to only know the rules.
“The young man knows the rules, but the old man knows the exceptions.” — Oliver Wendall Holmes —