Concept art is a highly competitive field. It seems like there is a never-ending pool of talent waiting to get in.
For myself, I hadn't really considered the field simply for that fact alone. As someone who is easily pleased in all sorts of art jobs, it felt like concept art needed more dedication just to get ahead of the pack.
I fell into concept art by accident, really. I had spent years doing illustration and felt comfortable spending hours on a watercolor or digital painting. The idea of constantly tossing away ideas- scrapping work easily and being OK with trashing hours of work, felt... odd.
Approaching concept art was entirely different.
To work in concept art, you need to be absolutely OK with continuously moving on.
You need to feel not just comfortable with scrapping entire art projects, but motivated by it.
Your technique, detail, and trying to impress is secondary to finding the correct design.
Illustration is none of these things.
Illustration is all about invoking a feeling, inspiring the viewer when they look at it.
It's about taking the time to perfect the line work, the layout, the lighting, etc.
It's less about the idea and all about the execution of technique.
To summarize, concept art is tossing whatever is in your fridge into the pan and hoping it will come out edible.
Illustration is decorating a cake in the hopes that the person it is for will turn to you, delight in their eyes.