In science history, there is a time called eureka moment, which usually describes that a person finds the answer to a problem. Though the moment is rare (maybe only a handful of times), when it appears, it will boost the science and technology. However, eureka moment may be unsteady. When something occurs to you, you may forget that at the next second. So we need something to record these wonderful thinkings. Fortunately, concept can be a substitute for our bad memory.

The express of a concept should be clear and unequivocal. Without that, people can hardly understand or grasp the concept. If the express is ambigious, it is easy to be under the illusion that they have known what this concept is (in fact not) and revel in that. Thus, people would resort to such wrong understanding to explain what they see. That would be exceedingly tragic.