Also, if you want to use the brush the entire time, instead of switching to the eraser, you can just fill a layer with black, and then add a layer mask to the layer. Then you can just switch between black and white with the brush tool. I use layer masks a lot, because I hate having to switch the different brush settings for the paintbrush and the eraser. Of course, if you like having different settings for both, you can still use the eraser and get the same effect with the layer mask.
"But... how does it feel? To just stop breathing?"
"Strange. You realize... just how much... effort... it has been... all along."
100 sketches in 100 days