It is not quitting and it is not a rebrand. A pivot holds one thing steady and changes another: same customers, different product; same product, different customers; same product and customers, different way of charging. The learning is the asset you carry across. Starting an unrelated business because this one is hard is not a pivot, it is a restart, and it forfeits everything you paid to find out.
The hard part is timing, and the honest signal is evidence rather than mood. Founders pivot too late far more often than too early, because persistence is the trait they have been praised for and each additional month feels like the one where it turns. Set the condition in advance — if retention is still below x by date y, we change direction — and write it down while you are calm. If you run several ventures, the same discipline applies per business; the strong one should not fund an indefinite refusal to decide about the weak one.
A concrete example: you build a time-tracking app for freelancers. Two thousand people sign up, almost none pay, and support requests are dominated by one question: can it produce a client-ready invoice. You keep the timer and the customers, drop the reporting features nobody opened, and rebuild around invoicing at $19 a month. Same audience, same insight, different product — and the eighteen months of user conversations are what made the new direction obvious.