Input = output
The idea behind the title is this: the quality of your input, determines the quality of your output.
I believe most of us want to make great stuff, produce art or work. I don't think anyone wants to make bad, low quality work on purpose. We try to give our best. We don't always give our absolute maximum, but we use the knowledge and skills available for us at that particular moment when doing our work.
By "work," I mean anything that is produced as art. A photographer takes pictures; a painter paints paintings; a carpenter makes things out of wood; a marketer does marketing. All of these can be viewed as art. Anything that doesn't have a map on how to do it is art. See my post "How to be an artist?" about this and find out more.
To become better at what we do, we have to get better input. This is where input = output comes in.
Let's take photography as an example. Many photographers get their inspiration from Instagram. Instagram is great, but it has some flaws when it comes to art.
Instagram is mixed with great art, bad art, baby pictures, memes, and cat pictures. The problem with this, especially for beginner photographers, is that separating bad art from good art is very difficult. Everything blends into one big steaming pile of mediocrity.
Getting all of your inspiration from the same place as everyone else is never resulting in you to produce anything more than mediocre work. You end up doing the same things as everyone else is doing, because that's all your mind has access.
What I'm pointing at, is that if the quality of your input is mediocre, then the output can't be anything more.
If you only eat junk food and drink sugary drinks, you can't possibly expect to have excellent health and great thoughts. If your brain gets low-quality nutrients, it won't be able to produce higher-level ideas. Yes, eating healthy is not only about weight loss.
The solution is to seek out high-quality input. Instead of watching TV, read a book or listen to an educational podcast. Instead of looking at pictures on Instagram for inspiration, read a photography book. I could go on endlessly here, but you get the idea.
Fix the input, and the output fixes itself.