Earlier quoted context omitted.
I'm an economist, yet I only recently realized that adjustable-rate mortgages are economists' consensus best choice for consumers. Based on the expectation that personal economics are well-correlated with broad market economics, and that interest rates will decline when the economy struggles.
Why don't you get fixed rate so that the rate never goes up. When the background rate goes down you refinance for another lower fixed rate.
Once fixed rates got down to the 3-4% range, that seemed to no longer hold and I was frequently offered fixed-rate jumbo mortgages at rates slightly lower than adjustables (I have no idea why they even bothered to quote an adjustable at that point).
If you could get a 10/1 cheaper than a fixed-30 and were pretty sure you'd be moving in 7 years, that's why someone would take out an ARM. (Or, if they could qualify for the ARM but not the fixed-rate payment.)