What should we compare? It is things between 'same' and 'different.' If you compare the same thing, only the conclusion that "it is the same" comes out. If you compare completely different things, you do not know what to look for in a lot of different features.

It is the wrong dichotomy that thinks that there is only "same" or "different."

In reality, it is gradational. There are exactly the same things on one end. There are completely different things on the other end. Between them, there are very similar things, most of the features are the same, but somewhat different. There are things which are not similar but with a little common part.

Fig: The boundary between "same" and "different" is gradational.

For a new pattern discovery, we need to compare things that are not the same and not different. We need to compare things some features of them are the same, and some are different. That is similar things.

Fig: Between "same" and "different," there is "some parts are the same, and some parts are different."

For a concrete example, imagine an electric drill. We can exchange the drill tip, the rotating part. Each of these tips is not completely the same, but the root part of the tips has the same structure so that we can insert them to the body of the drill.

There is a similar pattern to create interchangeable parts in the program. In programming language Java, we have the seams like structures "interface." It defines what kind of methods a class has. By this mechanism, you can exchange classes with the same interface like interchangeable parts. In physical tools and programming languages, there is a pattern that the seams of interchangeable parts have a common structure.