Heck, I've had one fail, a nursing home revenue bond but it was an insured bond if you're counting that as a failure. Didn't lose a cent. That was about 8 years ago. I didn't buy that bond. I inherited it. Revenue bonds are riskier, I know.
Puerto Rico tax exempts all crashed together a few years back. Bankrupted many people down there.
I'm more than willing to pay Vanguard 0.09% to do the paper work and research for me.
BTW, like you, I almost always hold to maturity. I can't recall ever selling a bond. I hold most of my stocks -- they're all blue chips -- for ages. Have owned some index funds for >30 years.
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Because the Good Life is Just a Pump or Two Away