Personas (read: people) change. Their behaviours change via increased or decreased interaction with your product and services. External forces are also at play (economical, technological, personal etc). It is completely naive to think that printing out a head shot with some personal details of some fictitious character will serve as the “north star” for your roadmap and product development. Yet so many companies are guilty of this.
The other thing I learnt is to design a few steps further. Working at a startup, the resources are limited. Your development team will probably have to implement the design in a few phases. But by examining your product roadmap, backlog, stakeholder and user interview feedback, it enables you to design a step or two further and allows the development team to leave space for the advanced features you have in mind.