Default effect
Etymology
From default, via Old French defaute, "a failing to act." Johnson and Goldstein’s 2003 study of organ-donation rates — vastly higher in countries where you must opt out than opt in — made it famous, and it became a pillar of Thaler and Sunstein’s "nudge" thinking. Same people, same forms; only the default changed.
noun · /dih-FAWLT ih-FEKT/
The tendency to stick with whatever option is preselected rather than actively choosing something else.
What it names
How enormous decisions get made by inertia — whoever sets the box that’s already ticked quietly sets the outcome.
Example
Auto-enrollment leans on the default effect: switch retirement plans to opt-out and participation jumps overnight.
Related idea
Status quo bias is the general preference for how things are; the default effect is that preference exploited by whoever designs the starting option.