They say that the purest knowledge is empirical, that is, based on direct experience. But experience can be deceitful, e.g. optical illusions or logical experiments of dual interpretation. After all, understanding is the primary of the mind and of it’s director: the reason.
A simple experiment: imagine the smartest man, the best mind system in the universe. That man needs to live and cogitate a little and then he’ll understand it all, a whole system will form in his head. It will be reflected, organized, prepared, and then be visible. But still the man needs at least a minimum of time to gain an experience of the actual and the reality in which the mind finds itself in order to reflect and formulate the cognition.
Reason and the power of intellect, packed in a well organized mind are the key crucial forms of knowledge. Logic, mathematics… But experience is still the highest, most important, practical way. Actually, cognition is a competent qualitative connection, refinement and reforming an experience into human knowledge.