Besides being a writer, I'm a foodie. I love cooking and have won many cook-offs and recipe contests. When I read a recipe I can tell immediately if it will work. This is far more crucial with baking than with cooking, because baking is an actual science. If you leave out the flour, say, it won't work. If you leave out even SOME of the flour, it won't work.
What does this have to do with writing? Flour is like discipline. You can have all the other ingredients (raw talent, ideas, an eye for detail, etc.) but if you lack discipline, you will never succeed at writing. Or singing. Or dance. Or art. Or sports. There are so many talented people out there WHO WILL NEVER MAKE IT because, despite being phenomenally gifted, they don't have the discipline to take their craft to the next level.
You can't just like writing. You can't just love writing. You can't just have a bucket full of terrific ideas. You must be someone who can roll up their sleeves, ignore the flu, hunker down, and work hard. Every day. Even when there's a chocolate silk pie in the fridge. Even when your best friend wants to go to lunch. Even when a new movie just opened. Even when it's a beautiful day to go sailing. All the talent in the world will not make up for the inability to sacrifice. And, oddly enough, a mediocre writer can actually surpass the talented one if he simply has that dogged determination to complete a task. Writing success, like baking success, requires the right ingredients. And discipline, like flour, is not one you can leave out.