Thoughts on new drawing

Last night I was talking with a friend about my drawing. During the conversation I began to form an idea in my head for another drawing. Later when I tried to go to sleep I kept on thinking about the drawing. Usually when I think about a drawing I want to do I just get a basic idea. But this was down to the last detail. Like the reflection of light off of a piece of metal, for example.

What sucks is that I was supposed to do a portrait for a friend of mine. It's a drawing I really want to do but I also want to do this one that's in my head. I know that if I ask the friend I'm supposed to draw for she would tell me to do the one in my head first. But I've put off her drawing a few times already for other stuff. So I feel bad.

I suppose I could work on both drawings at the same time, switching when I'm stuck or frustrated or just need a change of pace. But I don't like doing that. I prefer to work on one project at a time, devoting my whole self to it.

I'm going to do the portrait first because I've put her off for a while. Then I'm going to dedicate myself to this new concept because I need to get it out of my head and onto paper.