If the katana looked and felt great, and was easy to use, but broke into pieces during battle, you'd run out of users pretty quickly. The thing has to be solid, and give the user full confidence in its reliability. Craft is about details. The rounded corners and smooth edges. Making sure the pixels line up and nothing is out of place.
Precision is what creates energy and movement in a design.
Users may not notice in a conscious way, but they will feel the difference between getting the details right and having bits out of place. Error messages are always well considered. Transitions between screens or pages are smooth, and sound is used to reinforce the action and give subtle reinforcement about what's happening. Craft is about deciding to do less, if it means the quality bar for what is in the product is outstanding. Doing less facilitates greater focus, greater quality, and greater design.