Avoid quitting at the first sign of difficulty
Avoid quitting at the first sign of difficulty. This is so common place that a failure to persist turns into self-confirmation that not trying was the best option, which then turns into folklore and hearsay about the pointlessness of trying.
Anything worth doing or achieving is going to encounter hurdles and difficulties. Treat that as a given and treat the challenges as something that will test your mettle and shape you for the better, making you stronger, more astute and more compassionate. If at first you don't succeed, try it again and again.
If you don't get the job of your dreams or the publisher for your novel at the first, second or third attempts, make many more attempts. Too many people think that the first few rejections mean that it's never going to happen.
This is a self-limiting and baseless assumption; provided that you know your strategy or goal is right, it is simply a case of not repeating it enough times. Remember that there are a lot of people and a lot of opportunities in the world you can't possibly hope to pitch your own wishes and goals at the right people first off every time!