Think of an online businesses revenue and customer base as a snowball atop a hill. When you first start your online business core is small, core meaning your customer base and total revenue. As each month passes your core should become a little larger while you retain customers who have made past purchases. After all think about all the hard work that was done to acquire each customer and earn their trust. Certainly a percent of them will come back automatically and make another purchase do you not think? If you think that you will automatically retain your customers without any effort then you might be in for a surprise.
It would seem logical to think your business should have a 50%+ customer retention if you are selling a commodity-based product should it not? Something like shipping supplies, eatables, or household product with a part that is consumed over time like a refrigerators water filter. Well even if your business is not a commodity business, your product is used up over time you have more than a single item, something that people would find interesting enough to make another purchase? Now this snowball, or core customer base, might grow slightly over time but not the way it should with some effort.
Unfortunately e-commerce business do not put enough focus on customer retention, as you will see. Matter of fact business are spending far more in acquiring a new customer than it is retaining an existing one, which is significantly more costly. Matter of fact acquiring a new customer is much more costly than keeping an existing one. In a Forbes study about e-commerce business it found that the cost of acquiring new customers is 5 times the cost vs. retaining existing ones. There are several additional studies that even push that number to 8-9 times the cost.