Ease of use is often conflated with ease of learning, and usability is conflated with discoverability. But discoverability is only one part of usability, and it is easily possible for optimization of discoverability to produce poorer usability in other respects. A tool's design can be discoverable, and also annoying or inefficient. These flaws become relatively more important as people spend a long time with the tool, because discoverability becomes less important when you have less to discover.