Single-option aversion
A lone option feels risky; add a second and people commit.
What it means
The reluctance to commit to a choice when only a single option is presented, such that adding even one more alternative — without changing the original — increases the likelihood of choosing the original. The driving force appears to be a desire to compare: a solitary option offers no way to gauge whether it is a good deal, so people defer, search further, or decline, whereas a second option provides the comparative context that licenses a confident decision. The effect is distinct from, and can run opposite to, choice overload, highlighting that the relationship between the number of options and the propensity to choose is not monotonic. It matters for retailing, fundraising, and choice architecture, where offering a single 'take it or leave it' option can suppress action that a small, comparable assortment would unlock.
Examples
Shoppers shown one DVD player are more likely to wait than those shown the same player alongside a second model, because the pair lets them judge value.
A donation page offering only a £25 button raises less than one offering £15 and £25, because a lone figure gives no way to tell whether it is generous or steep.
A hiring manager shown one strong candidate keeps the role open 'to see who else is out there'; shown the same candidate beside a weaker rival, they make the offer that week.
First described in Mochon (2013).