Business model viability, in the majority of startups, will come down to balancing two variables:

-Cost to Acquire Customers (CAC), and,

-Lifetime Value of a Customer (LTV)

Successful web businesses have long understood these metrics as they have such an easy way to measure them. However there is a lot of value in looking at these same metrics for all other businesses, especially in the SaaS model.

It doesn't take a genius to understand that business model failure comes when CAC (the cost to acquire customers) exceeds LTV (the ability to monetize those customers).

A well balanced business model requires that CAC is significantly less than LTV

Image source: //www.forentrepreneurs.com/startup-killer/