The finances of banks are highly counter intuitive. Customer savings (bank deposits) are a liability to the bank, NOT an asset (as one may mistakenly think) to the bank as they have to be repaid at any time (customer withdrawal); the assets of a bank consist largely of loans made to individuals or companies, since they too will be repaid with interest over the period of the loan. However those debtors (borrowers of the banks, such as companies or individual) may not have the liquid cash to repay the bank loans (100% loan repayment on a mortgage is not always practical, so if the bank demand the loan or mortgage to be repaid immediately, that is a tall order), thus any run on the bank (customer withdrawals) will create a huge potential problem for the debtors of the bank (individuals or companies who have borrowed money). The run on the bank will result is the bank demanding immediate repayment of the loans or mortgage to be repaid, refusal to refinance loans when they become due, or simply charge a higher rate of interest and impose more stringent conditions when the loan is renewed.

This explains why problems for the banks ripple throughout the wider economy.