When interest rates go up, the mark-to-market price of older, lower-rate bonds goes down since you can get higher coupons (better interest rates) by buying newe

When interest rates go up, the mark-to-market price of older, lower-rate bonds goes down since you can get higher coupons (better interest rates) by buying newer bonds. If you "Hold to Maturity" (HTM), it won't matter -- you'll eventually reclaim the entire par value of the bond. But if you all of a sudden start selling them, you're going to realize massive losses. So when you buy the bond, you better be really sure you can HTM, or you'll eat your shirt. Here's the kicker: SVB bought at the "top" -- at a time where rates could only increase (zero percent rates), at all-time high home prices (MBSs), all while The Fed indicated that they'll keep raising rates until the economy cries 'uncle' and the yield curves were inverting. That's why they were risky.