It's mainly the jagged characters on the screen. To create text, those straight-sided squares butt up against each other. Tech types call it bitmapping. Letters like F and L look fine, because they are straight. But when it comes to the curves and diagonals that build 20 of our 26 capital letters and 23 of the lowercase ones, pixels fall flat on their geometric faces.
Heavyweight thinkers whine about the bitmap jaggies.
Negroponte argues that screen images should be nothing less than print quality. High-resolution monitors, which add more pixels, help. But they aren't cheap. It makes characters easier to read, paradoxically, by making them less sharp. To understand the concept, look closely at a magnified capital letter X .