Wisdom is not wisdom when it is derived from books alone.

Reading hands you conclusions without the cost that produced them, which is efficient and also the whole problem. You can hold an accurate principle in mind and still fail to recognise the situation it applies to, because recognition is trained by having been there, not by reading. The book supplies the answer and life supplies the moment when an answer is needed. Only one of those can be studied in advance.

Take a principle you believe and find where it has actually been tested in your own conduct. If it never has, hold it as a hypothesis rather than a conviction. Convictions ought to have some mileage on them.