I have my own definition of analogy. I do not apologize. I use analogy only when the two things being compared share an underlying structure.

Yes, well, in that respect, and many others, American high schools do rather resemble prisons. (Turtles All the Way Down, Green, page 11)

Several resemblances were then considered. The point is this. If there are several resemblances between prisons and schools, there may be a reason for those similarities. A reason will be something the two share in underlying structure.

When two things are similar in more than one way, look for some underlying structural similarity.

The underlying structure might already be implied or understood. But when it isn't, you should seriously consider including it – the underlying structure is probably the most important point about what you are trying to say.