An art teacher told me what is kind of obvious: things aren't outlined in the real world. Painting a still life — the apple is in fact simply defined by where the apple color ends and the bowl color begins.

To be sure, when we start sketching we would probably find it convenient to make a little arc on the page that delineates the boundary of the apple but by the time you move to finishing the piece (if realism is what your going for) a line of any thickness delineating the apple should be gone.