Profit and loss is the heart of business and economic change. Entrepreneurs drive the market at every level, predicting future wants and taking risks with their property. Earning profits is never guaranteed.
Deposit banking rests on the bank honoring property rights. Loan banking rests on making good loans that will pay off. But when loan banking and deposit banking merged, the temptation to loan out much more than was actually in the bank arose.
Austrian economists differ from mainstream economists mainly in this way: they do not rely on mathematical models, but on understanding what causes success or failure in the real world. Opportunity costs determine the choices people make.