A lesson is easier to carry when it is offered without a performance of superiority.

Advice arrives carrying a status claim whether you intend one or not. A tone that stresses how obvious this is, or how long ago you learned it, asks the other person to accept a position underneath you as the price of the information, and many will decline the whole package rather than pay. The content might have been excellent and it never gets used.

When you know something useful, hand it over flatly and briefly. Mentioning that you learned it the hard way, and leaving out how long ago, makes the same lesson much easier to take.