December is a great time to take a vacation. It is a terrible time for the Federal Reserve to raise interest rates.

The most obvious reason is because, well, many people go on vacation and are therefore out of the office. Why would the Fed want to wreak havoc on their time off? And think of the hard-working souls left in the office; they'd have to deal with the messy aftermath of the first interest rate increase in almost a decade, which would surprise much of the bond market.

The less obvious, yet more salient reason is that December is when banks tidy up balance sheets, strip down risk, close out books, and prepare for a final year-end stress test by regulators. That means traders at big banks aren't going to be as willing to facilitate big Treasury and other debt transactions, leading to bigger price moves if the Fed acts.