How is the atp produced in glycolysis like earning a return on an investment ?

Glycolysis is the first step of cellular respiration - the process comprised of series of reactions in which energy is extracted from glucose molecules. The process of glycolysis is almost same in all living organisms.

If we quickly overview the process of glycolysis, we see that it is a process of earning ATPs as a return on ATP investment, why?

Therefore,total amount of 2 NADH and  4ATP molecules are produced.

But since, there was an investment of two ATPs during the preparatory phase of glycolysis. Therefore, a total of  4-2=2 ATPs is formed/ So it is like an earning on an investment.

Hope it help!