Typically, you have to live out the words of the advice before honestly coming to understand them. Advice -- especially great advice -- is often received as theoretical, removed from specific context, and thus filed away in the deepest recesses of the mind. It doesn't come back to top of mind until a specific situation is encountered, and the advice is suddenly recalled. Then it clicks.

Theoretical advice is generally incomplete unless/until activated by personal context. Advice isn't a substitute for experience, but rather, a framework through which to process experience.