Over the past few weeks I've described in depth responsibilities of a product manager and I hope you now understand these responsibilities are plenty. Imagine now a small start-up. The founder has been in the market for years and she knows all the competitors first hand. She has been dreaming about the product for a long time and she knows exactly what she wants. She knows her technical co-founder from her previous job and they've discussed user stories over lunches several times over. They share the same dream and when a feature is completed, there's no need to spend much time discussing it, it's done exactly as both founders have imagined it. And since all the stakeholders share the same table, communication is instantaneous. Basically, all the people at early start-ups do is analyze product performance and dream about glorious future. Eating your own dog food is a given. No wonder then that start-ups are so much more successful at product development than bigger companies.
Now imagine the same start-up seven years later. The company has managed to survive and gained some traction in the market, but it hasn't really succeeded. It's still wildly ambitious and designed for growth, so it still likes to call itself a start-up. But with dozens of people around, developing products is no longer a two-person affair. Each of the responsibilities that a product manager should do suddenly starts taking an awful lot of time as it starts involving increasingly more people. Frustrations start to grow as founders and early employees cannot grasp why with more people the companies seems to be producing less than at the beginning. So the requirements on the product manager's responsibilities are gradually reduced in order to accommodate the same "productivity" as before. Cutting out any of the responsibilities eventually cause either wrong product direction, poor productivity of engineers, misalignment with the business side of the organization, or disconnect with the market. And then the product manager is the first to be blamed and the first to be fired.
Development of products takes a lot of time. In my opinion some five times more than a regular engineer or business person anticipates. If you can't afford to spend that much time on product development you better find yourself another business. Or keep producing even more unsuccessful shit.