The average rate on the popular 30-year fixed mortgage has been so low for so long that a good chunk of borrowers can't even contemplate the idea of it ever going higher.

Why should they? Every time we warn of rising rates, or see a tiny bump up, some global economic tantrum pushes them back down. Most borrowers have refinanced to take advantage of these low rates, but, strangely more than 1 in 10 have not. These borrowers have rates above 5 percent, while the rest of us sit around 3½.