You know how advice is - you only want it if it agrees with what you wanted to do anyways. - John Steinbeck
Advice has value only when the recipient sees themselves as having something to learn. This state of openness, of humility, is so uncommon, the act of giving unsolicited advice will almost always fall on deaf ears. In fact, the obvious intimation, that the recipient does not already know what they need to, that they should be humble and accept this wisdom, is almost always taken as an insult.
I’m inclined to avoid the practice of giving unsolicited advice in almost all cases. When there is a fiduciary responsibility and a measure of mutual respect, such as exists in good employer-employee and parent-children relationships, then, by all means, give your best advice. But with acquaintances, love-struck buddies, or teenagers, it’s probably best to shut your pie-hole.
I recently came across the phrase, “You only understand what you know”, and I think it applies here. It essentially means that there are certain concepts that a person cannot comprehend until they have reached the appropriate state. It just doesn’t fit in their head - they lack the language, the need, whatever, to give that concept meaning. Let me coin a simpler version: “You can’t teach a tadpole to hop.” It doesn’t mean there is anything wrong with either you or the tadpole. It just means that, at this time, there is no context for progress on that matter.
One might also extend the metaphor to note that it is quite possible that, with or without your assistance, the tadpole very well might learn to hop on its own. That’s probably better for all involved, anyway.