这本书的标题来源于一个古老笑话的妙语，它是这样的：
乔是一个非常和善的人，但是他思考总是有点慢。他走进一家商店，一群人正围观售货员和他旁边的肥皂盒。推销员正在推销一个新奇的发明——热水瓶。他说，“它能保持食物的温度……”乔想了一会，对这项新发明感到惊讶——它能够根据你放入的食物种类来决定应该做哪样事情。他无法抑制自己的好奇心，手舞足蹈的说 “但是，但是，但是，但是……”最终，他脱口而出，问出了那个急切的问题 “但是它怎么知道的？”
不管你笑没笑，问题的关键是乔看到了这个热水瓶的功能，并认为它一定能够感觉到瓶子里的东西，再相应地执行加热或冷却操作。基于这种想法，乔认为它必须包含有一个加热器和一台冰箱。他不知道热水瓶应用的是一个简单的原理，那就是热量总是试图从较热的区域转移到较冷的区域，热水瓶所做的只是减缓热量的散失。对于冷的内容物，热水瓶会减缓外部热量的进入，而对于热的内容物，它会减缓内部热量的散逸。热水瓶不需要为了完成它的使命而 “知道”，也不需要加热或冷却任何东西。最终，无论冷还是热，内容物的温度都会统一到室温。故事或许很简单，但是乔关于瓶子是如何工作的思考比现实要复杂得多。
所以我们为书起了这样的书名。当谈及电脑时，人们通常会观察它们的行为并基于此想象这些机器里一定有的各种各样的东西，亦或者想象着它们必须遵循的各种原则，以及它们能够做到的事情。人们有时甚至会赋予机器人类的品质。当然，一些人后知后觉的为自己的想象感到尴尬，就像我们在笑话中的乔一样。
计算机实际上很容易理解。当然，计算机有比热水瓶多得多的部件，但是每个部件都非常简单，并且它们的运行都遵循着简单易懂的原理。
热水瓶所遵循的的原理是热量的运动，这是我们在生活中可以观察到的现象。当冰块从冰箱中取出时，我们看到冰块在逐渐融化；当家人晚餐迟到时，我们会发现桌子上的饭菜已经凉了。
在计算机中，它的工作原理与电力有关，但这并不意味着很难理解。如果你观察到当你打开电灯开关时，灯泡会亮起，而当你关闭开关时，灯会变暗，这就是你观察到的计算机运行的原理。这就是你需要了解的所有关于计算机的电力的知识。
原文：
Introduction
The title of this book is the punch line of an old joke that goes like this:
Joe is a very nice fellow, but has always been a little slow. He goes into a store where a salesman is standing on a soapbox in front of a group of people. The salesman is pitching the miracle new invention, the Thermos bottle. He is saying, "It keeps hot food hot, and cold food cold...." Joe thinks about this a minute, amazed by this new invention that is able to make a decision about which of two different things it is supposed to do depending on what kind of food you put in it. He can't contain his curiosity, he is jumping up and down, waving his arm in the air, saying "but, but, but, but..." Finally he blurts out his burning question "But how do it know?"
You may or may not have laughed at the joke, but the point is that Joe looked at what this Thermos bottle could do, and decided that it must be capable of sensing something about its contents, and then performing a heating or cooling operation accordingly. He thought it must contain a heater and a refrigerator. He had no idea of the much simpler principle on which it actually operates, which is that heat always attempts to move from a hotter area to a cooler area, and all the Thermos does is to slow down this movement. With cold contents, the outside heat is slowed on its way in, and with hot contents, the heat is slowed on its way out. The bottle doesn't have to "know" in order to fulfill its mission, and doesn't heat or cool anything. And eventually, the contents, hot or cold, do end up at room temperature. But Joe's concept of how the bottle worked was far more complicated than the truth.
So the reason for the book title, is that when it comes to computers, people look at them, see what they can do, and imagine all sorts of things that must be in these machines. Or they imagine all sorts of principles that they must be based on, and therefore what they may be capable of. People may assign human qualities to the machine. And more than a few find themselves in situations where they feel that they are embarrassing themselves, like our friend in the joke, Joe.
But computers are actually quite easy to understand. Of course computers have a greater number of parts than a Thermos bottle, but each part is extremely simple, and they all operate on a very simple, very easy to understand principle.
With the Thermos, the principle is that of the motion of heat. This is something we can observe in life. We see ice cubes melting when they are removed from the freezer, and we see the hot meal cooling off on the table when the family is late for dinner.
In the computer, the principle on which it operates has to do with electricity, but that doesn't mean that it is hard to understand. If you have observed the fact that when you turn on a light switch, a light bulb lights up, and when you turn the switch off, the light goes dark, then you have observed the principle on which computers operate. That is about all you need to know about electricity to understand computers.