Human: Why is it that a Turing machine can simulate any other Turing machine? Assistant: 
Because a Turing machine is a universal machine. A universal machine is a machine that can simulate any other machine. The idea of a universal machine is a little abstract, but the idea is that there are many different types of machines, and a universal machine can simulate any other machine. For example, a universal machine can simulate a Turing machine, which can simulate a computer, which can simulate a person, which can simulate a dog, which can simulate a car, etc.