First, there’s generic advice. The kind that fills books and graduation ceremonies. It represents the advice-giver’s accumulated wisdom, but it’s not directed to an individual.
Confucius shared general principles of good living, not just advice for one person. Steve Jobs spoke  to the entire Stanford convocation, not just one graduate.
The advantage of generic advice is scale. Instead of reasoning about all cases and circumstances, the advice-giver tries to provide a best-fit approximation of the advice for most cases. The advice is better the closer you are to the author’s ideal case.
Because of this scale, through books we can access the recorded generic advice of the best thinkers who have ever lived. It doesn’t matter that Seneca died thousands of years ago, I can still draw lessons from his teachings to apply to my own life.
The disadvantage of this advice is that the more nuanced the situation, or the further removed you are from the ideal case, the worse the advice is. Seneca couldn’t have anticipated how life has changed in modern times, nor could he anticipate all possible permutations of life situations.
The Importance of Specific Advice and Mentors
I love generic advice. It’s probably the reason I read so many books. But the problem with this advice is that sometimes it doesn’t work. You may try your best to implement the suggestions of one author, only to find them useless. Worse are the generic platitudes or advice which is correct “on paper” but fail to accommodate the endless nuances of reality.
That’s why specific advice is crucial. Specific advice allows you to tap into the tacit and nuanced knowledge of someone who has been there before. It’s the difference between reading a book on calculus, and having someone show you exactly why you got a question wrong.
Institutions like universities are mostly about facilitating this specific advice. With Wikipedia, cheap textbooks, libraries and Google searches, generic advice large enough to fill entire lifetimes of education is freely accessible. The gap being filled isn’t the knowledge, but the specific advice that is sometimes missed in a textbook.
Because specific advice is so valuable, it helps explain the importance of “who you know over what you know” to fields like business. Because the generic advice is too simple to fill all the gaps. Ben Casnocha  puts this another way in saying, “the who you know is the what you know.”
A realization that made a big difference in my life was that, just as I can read books in a library, I can go find mentors to help me. Too many people put arbitrary limits on who they can attempt to reach out to or ask advice from, and as such, never get the benefits of having someone experienced give them a push in the right direction.
Admittedly, the higher you aim your sights, the harder it can be to make a deep connection. People are busy, so they won’t always return your emails or calls. But for whatever pursuit you’re trying to excel at, there are thousands, if not millions of people who have done it before. The stupidest thing you can do is not even try to talk to any of them.