Customer acquisition funnels are multiplicative (E.g. Ad -> Landing page -> Signup -> Trial -> Actual product usage -> Purchase). Double any factor along the way, and the final output doubles. But it also means that if any factor along the way is 0, you get nothing out in the end. That can be incredibly demotivating when you're first starting out, because you don't get any payoff (or money to pay yourself or employees with) until you've made every factor non-zero. It also means that as long as any factor is zero, attempting to optimize any factors downstream from that is basically done in the blind (i.e. improving the product when you still don't have anyone even getting to your landing page).