The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires. - William Arthur Ward
When learning new things, or entering a new field of study, YouTube is one of my first go to destinations. Not just because visual components can really add to the learning experience, but for the reason in the quote mentioned above - a boring book with tons of information on a subject that doesn't get you excited, is not going to make you into an expert in that subject, because you won't be motivated to pursue it. Someone who on the other hand doesn't give you much beyond the basics, but inspires and motivates you to continue and learn of your own accord, will then encourage you to keep learning until you master whatever it is you've come to learn.
I've learned from and been inspired by the likes of Tim Schmoyer, Roberto Blake, or Derral Eves with their YouTube growth videos and know how. I was inspired to finally go ahead and start my channel by a mixture of people, including a particular video about starting a YouTube channel made by InfiniteWaters a few months ago - within a few days after watching it I'd bought my microphone and got started on my first video.
I've been inspired by tons of the great TED talks out there on a wide range of subjects.
I've also been inspired by other self-development professionals who do what I'm now trying to do with my channel, i.e. motivate people to improve and succeed. People like Tony Robbins for example.
My working out and self-improvement health wise with my diet etc has been motivated by the likes of Elliot Hulse and his videos.
There's a whole lot of really inspirational life-changing material on YouTube. If you look around for a little in any particular section you're interested in learning about, you're bound to find an awe-inspiring teacher or mentor there somewhere!