[chernevik]

The whole point of a bank is maturity conversion, the transformation of short-term deposits into long-term loans.

It generally works because while any one depositor's funds are short term, the pool of such deposits is generally stable. A good chunk of today's deposits will fund tomorrow's withdrawals. Banks also have elaborate instruments like commercial paper and the Fed discount window to cover short-term liquidity gaps. A bank with assets it can't sell quickly enough can generally borrow briefly from some other bank to cover the term gap. But there is a limit on how much such borrowing a bank can do, and SVB has hit it.

It seems that SVB made a classic mistake of putting a lot of "hot" money into long-term assets, thus taking on interest rate risk. They probably should have put the surge of deposits into shorter-term instruments, but that would have forced them to reduce interest on deposits or their own profits.