Financial Economics and Corporate Finance
This is referring to a general principle in finance. What matters most is the assets you have and the things you invest on, not really the way you finance these investments.  In the balance sheet, the asset side has the information about the assets you have, while the liability side has information about how you financed them. 

This general principle comes from a very powerful idea called "the efficient markets hypothesis". Miller and Modigliani showed that if the financial market is perfect (basically if it has no private information, transaction costs, taxes, etc), the overall profitability of an investment does not depend on how it is financed! 

Of course, markets are not perfect. However, many many studies have documented that most of the time, the financial market is pretty close to being perfect, especially in developed economies like the  US. So financing decisions do matter, but investment decisions matter a lot more.