I started out with books and when I feel I need to learn a new technique or pattern, it is usually still the written/illustrated word I rely upon, whether printed from a web site or taken from a book.
I've never learned a thing from a tying video or DVD, although I'm sure lots of folks have/do. This may be partially a generational thing. I just don't use videos for this sort of thing. I like having a book in my lap so I can occasionally dump the cuttings out of the binding onto the floor. You can't do that with a DVD player..
So far as "knowledge from many years of doing it", that's part of it too. But perhaps in a different way than you might think. There are a finite number of techniques that can go into tying a fly and once you have a fair command of any one of them, you'll be able to use that one to tie new patterns regardless of their material composition. For example, there is a way to tie in a down wing on a fly and with minor variations, it is the same whether you are making an elk hair caddis, a Coachman wet or a marabou wing for a streamer. And whether the wing is made from bleached zebra hair, saran wrap or plain old bucktail or elk hair, the technique is pretty much the same.
And so forth...
Eventually (and sooner than you might think) you find that 90%-plus of what you tie, you just tie. Without any book or DVD or any of the rest. It's already all between your ears.
If you're a new tier, learn your basic techniques well. Tying in a wing, dubbing, finishing a head, ribbing and all the rest. One you learn one, you'll always have it and each has a multiplicity of applications for hundreds of patterns.
That's the best advice and the best answer I can make to your question..