The Valley of Death must be small. Most VCs will not fund a company that spends too long with low revenue or few users. This is another manifestation of the timescale constraint.
Growth must be monotonic (always going up and to the right.) In rare circumstances a startup can survive flat or declining growth for a period if its management had the foresight or luck to raise funds before the lackluster growth that last until the growth resumes up-and-to-the-rightness.