A new product has no users, so all the focus is on acquiring new users.

Whereas a product with lots of users has a bigger focus on retaining the users already here.

If the focus continues to be on acquisition and not on retention, then there is a leaky bucket. 

Whoever ends up being acquired as a user, is probably going to churn and leave soon as there is no focus on retention.

Our habits and routines are not very different.

When we have none (or none that we want to retain), then the focus is on acquiring new habits and routines. 

But pretty soon, that needs to turn into retaining what we have acquired. 

Two weeks into the new year and new habits and new routines, it is already time to start thinking about how to retain what we have picked up and not lose them easily.