Young children have the ability to learn anything. What they learn without any effort at 2, 3 or 4 years old is later given to them with difficulty or not at all. What adults master with difficulty, children learn playfully. What adults absorb at snail speed is given to children almost instantly. Adults are sometimes lazy to learn while children are always ready to learn. And he claims it unobtrusively and tactfully. The material is simple, straightforward and crystal clear.