People paid less to lie about a boring task ended up believing the lie more
In Festinger and Carlsmith's 1959 experiment, subjects did a tedious task, then were paid either $1 or $20 to tell the next participant it was fun. Those paid just $1 later rated the task as more enjoyable than those paid $20. With too little external reward to justify the lie, their minds resolved the discomfort by changing their actual attitude instead.