Question

Comparison between two things cannot be made unless they are really alike

Answer 1

Two things can be compared only when there is some similarity between them. For example, it is not possible to compare a car with a walnut.

An analogy is a comparison of two objects or systems of objects which shows the ways in which they are considered to be similar. Sometimes the things which are being compared may be quite different but analogy highlights the ways in which they are alike. 

It plays an important role in decision making, problem solving, perception, argumentation, generalization, creativity, memory, invention, explanation, prediction, communication, and conceptualization. 

Answer 2

A comparison between two things can be made only if they have a common feature or attribute that can be compared. This can be any characteristic such as shape, size, weight and so more. Moreover, the two things being compared must be of the same category. For example, you can make a comparison between two fruits based on their characteristics such as the ones mentioned. On the other hand, you cannot compare a stationery object with an edible item.