The single-minded proposition (SMP) is the one idea the audience should take away — expressed in a single sentence, with everything else deliberately left out.
Sometimes called the key message, the "one thing", or the proposition. Its power comes from subtraction: an audience that is told five things remembers none of them.
A strong SMP is written from the audience's point of view and would be false for a competitor. "We are innovative and customer-focused" fails both tests.
If stakeholders cannot agree on the SMP, the creative work will not resolve the disagreement — it will expose it, expensively.