Modern, behavorial economics looks at how people are systematically irrational in their choices. Why You Waste So Much Money gives some examples:
A three-year study of about 8,000 gym-membership records from the Boston area found about 80% of gym members with a monthly contract were paying significantly more than if they had gone on a pay-per-use basis. That’s because members went to the gym an average of less than five times per month, far less than they thought they’d go. The result: Average users paid $17 per workout — even when a $10 ‘pay per use’ option existed. That adds up. Members were losing about $700 over the life of the gym contract, compared with the pay-per-visit option.
[...]
“Zero percent” teaser-rate offers on credit cards are a telling example. Consumers often choose cards with the lowest teaser rates, ignoring the fact that they may be paying 15% or more after the teaser rate expires. That’s because they vow to switch their debt somewhere else when the introductory rate expires. However, most people fail to transfer their balances. Customers should pay more attention to how long the teaser rate lasts, and to the rate that kicks in after the teaser rate expires.
Of course, I was spending something like $15/month for my gym membership and going three times a week. (Now I lift at home, when I lift…)