Reading something once and twice does not mean grasping the full meaning and getting to the core of the idea. Skimming and scanning are reading techniques that use rapid eye movement to move quickly through text to get a general overview. Reading rapidly to find specific facts does not imply full comprehension. Most people think that they understood something by skimming it for a few seconds. Comprehension is a different subject. It is the ability to process an idea or a text, understand its meaning, and make conclusions.