Sir Isaac Newton observed an apple falling to the ground, which led to the discovery of the law of gravity. An apple falling to the ground is a natural occurrence. However, it made Isaac Newton think, especially since the moon stayed in place and didn't fall. In daily life, we encounter many problems or challenges that make us think. Crossword or number puzzles and simple mathematics problems involving addition, subtraction, multiplication or division take our time and attention, according to Ki. Sign in to read more..