Why do teams slow down?

So, here you are. You just joined a team, you’re the third or fourth member to join and you feel good. Your team follows an Agile development method. You churn out new functionality and customer-value at the end of every iteration and things could not go any better for you.

The product sells, the team starts to grow to cover for the pressure of the increased “needs” or “features” and you start to feel an itch. The way you used to work does not scale anymore. You start feeling that your work is not that productive anymore. Maybe the meetings start to last longer, maybe the requirements are not that clear, maybe it is the product manager’s fault. To be honest you just don’t know why. The only clear thing is that your team is now bigger and less productive. What happened? What brought your team to this point? What’s keeping you back? Why can’t you produce as much as when the team was smaller? It can’t be the size of the team, I mean the Agile gurus keep saying that 7+-2 is still ok for a team size and you just got your 10th team member last week, it cannot be the team size, right?

Well, this description is based on true stories. In your company this has probably happened (at least once), so why did it happen? What caused your team to be “slower” when it started growing (even if not above 9-10 people)? Let me know, write a comment to this post and let us know what caused the slowness in your team.