The jāmiʿ (الجامع) is the relevant relationship that justifies coordinating two independent judgments. Two individually grammatical sentences do not automatically form a rhetorically coherent coordinated statement.
Inspect both the subject (المسند إليه)—what is being spoken about—and the predicate (المسند)—what is attributed to it. The bond may come from a shared subject, a relation between subjects, or a meaningful comparison between predicates.
A practical sequence is:
1. Identify the two independent judgments.
2. Identify any relation between their subjects.
3. Identify the relation between their predicates.
4. Decide whether that relation is genuinely intended by the context, rather than imagined as an arbitrary excuse for adding wāw.