The first time read Steven Pressfield's 'The War of Art' I had a real eye-opening moment. In the book he talks a lot about a thing called Resistance. He describes it well, so well in fact that when I realized what he was talking about I couldn't help but see my own mind in a whole new light, a light that I haven't been able to turn off since.
Resistance is the voice you hear saying "no" in your head every time you think about doing something creative, or challenging, or something you want to do in your heart. It uses all the power it has to convince you that it's not a good idea, that you'll fail, and that everyone will laugh at you and that you will lose everything if you even try.
"Don't write that book. It'll be bad. No one will read it. You'll be the subject of public ridicule."
"Don't start that business. It'll fail. Your wife will leave you. You'll have to work 12-hour days that will never pay off. It's not worth the trouble. Your current boss isn't that bad compared to this."
"Don't move to New York. You won't make it. The locals will notice instantly you're a tourist and you'll be robbed and people will throw half empty takeaway Starbucks coffee cups at you. You'll be ridiculed."
It'll do whatever it takes. The more you want something, the harder it'll fight. But the truth you must always remember is that if you listen to it, you will never make anything of your life. Perhaps no one can laugh at your book - but that's only because you never wrote it. And now you'll never know if it would have been a huge success.
Pressfield cleverly makes Resistance seem like an external entity, like a 5-year-old toddler who just happens to have landed in your mind. This helps you ignore it. After all, it's not really you. It's some random 5-year-old toddler.
Don't take advice from a toddler. He's got no experience to back it up.
P.S. 'The Art of War' by Sun Tzu is also good reading.