An alleged analogy may argue: “Case A has a ruling; case B resembles A; therefore B has the same ruling.” This is incomplete until the resemblance is shown to concern a legally operative common cause. Color, shape, or an incidental similarity is not sufficient.
Ask whether A's ruling is established, whether the proposed cause is truly effective, whether B shares it, and whether a difference or impediment defeats the inference. Objections such as farq, naqd, and mu'aradah can then test the reasoning. A well-formed qiyas survives relevant scrutiny.