Why is there only one button under Apple's phone?

In fact, Apple's mobile phone has only one key, not because it looks good and convenient. In fact, Jobs is a man who is very proficient in human nature. He wants to make things as simple as possible, even a child can use them. When there is only one button, you have no choice but to press that button. When you press it, it will have different interface displays or prompts to guide you to follow his steps. If you have three buttons like an ordinary smart phone, to be honest, you don't know which button to press without using it. Pressing two wrong keys in a row can't unlock the phone, which is very annoying. Suppose you buy a product and can't use it, will you feel helpless and crazy? Once this feeling is established, it will be bound to this product, which will lead to a bad impression of this product by users.