The most common reason a first version disappoints is that it tried to do too much. Six months of building, and the thing that was supposed to be validated in eight weeks is still unfinished.
The one-sentence test
Write down, in one sentence, what a user must be able to accomplish for this product to be worth using. Anything that is not on the path to completing that sentence is not in v1. Not "later in v1" — not in v1.
Things that feel essential and are not
Admin panels. With ten customers, you can edit the database directly. Build the admin panel when manual work becomes the bottleneck.
Multiple user roles. Ship one role. Roles multiply permission logic across every screen and every endpoint.
Settings and preferences. Pick sensible defaults. Every toggle is a branch you must design, build and support forever.
Onboarding flows. With your first users, you can onboard them personally — and learn far more from doing it.
Things people cut and should not
Authentication done properly. Retrofitting security is expensive and dangerous.
Basic analytics. Shipping without instrumentation means you cannot tell whether it worked, which defeats the point of an MVP.
Error handling. A crash on first use is a user you never see again.
Payments, if you charge. "We will add payments later" usually means never validating that anyone will pay — the single most important thing to learn.
A useful rule
If removing a feature would not stop a user completing the sentence you wrote at the start, remove it. You can always add it in week ten when a real user asks.