One thing that is worth mentioning, and probably poorly understood, is the difference between capital gains in the bond market and other kinds of capital gains.
Bond gains driven by declining market interest rates are not Mana from Heaven. They are an advance on future coupon payments. The only way we can pocket those gains is to leave the bond market.
Consider a 5% 10-yr bond issued at par where the yield drops to 2% day one. The price of my bond increases from $100 to $127 . . . weeeeee! I've just made a 27% annual return on my 5% bond and feel terrific. But the bond only promised me a return of 5%. So what happens?
Fast forward to the end of year 1. I get paid a $5 coupon, but a strange thing happens to the price of my bond. Even though market interest rates haven't changed, the market value of my now 9 year bond has dropped ~$3 to $124. Next year, I get another $5 coupon but my bond price drops another ~$3. That keeps happening until maturity, where I get back my original $100 face amount with no premium. So did I actually have a gain on these bonds? Only if I got out of the bond market.
We can rejoice for the time being that our portfolios have been fattened by the lower interest rate fairy, but the truth is, if we continue to hold those bonds we'll eventually give back 100% those gains. We're only going to earn our stated yield, and not a penny more.
This is probably the best explanation I have read regarding why bonds behave the way they do inversely to the rate.