Elizabeth Warren's September 12, 2019 debate retort that implied Americans lose little if and when forced to change health insurers because nobody really like their health insurer brought a laugh at the time. And, yes, she was partly correct and partly incorrect. Those folks clinging to their current insurers often fear the unknown more than the devil they know or the devil they think they know, given the data on how many Americans do not understand their own health insurance.
So, why prefer the devil you think you know or you know? The devil you know proverb is apparently Irish in origin and can be found in print as early as 1539. Prefering something you don't like to the unknowable is probably pretty powerful sentiment in health insurance decisions, backed by data showing that many are loathe to switch plans even when their current plan appears to serve them poorly, because of our system's mind-boggling complexity. The complexity itself may be no accident as it serves to bind those with fear of change to the existing plan as well as to thwart direct product comparison.