# Extending Ideas to Broader Classes > The concept of zero was difficult to grasp for people who had used counting only to keep track of the number of animals killed or the number of days passed or the number of units traveled. This is such a powerful concept to keep in mind. Consider the ways in which this comes up in general mathematics. The exponential comes to mind. It was first meant to capture the repeated multiplication of a number. But then we wished to extend it to decimals, and finally irrational numbers. This required that we find a definition that *held for our original case*, but importantly also held for our more exotic cases. --- Date: 20220117 Links to: [Big Ideas MOC](Big%20Ideas%20MOC.md) Tags: References: * Against the Gods: The Remarkable Story of Risk