Painting has taught me an annoying lesson: it still takes two coats of paint to cover one shade of white with another shade of white.
Case in point, our ceiling is painted White Truffle and the crown molding is painted Clear Moon. The only way I can explain the shade difference is, well, White Truffle is kind-of darker than Clear Moon. Let me stress the word "kind-of" because they are barely different.
Yet they are different enough to allow the Clear Moon to bleed through the White Truffle. Result of this interesting phenomenon: I have to go around the ceiling, twice, with a one inch brush because anything wider is too messy for freehand.
At least my freehand skills have greatly improved as a result of the painting project that never ends. It goes on and on, my friends.