Steve Martin, co-author of Yes! 50 Secrets from the Science of Persuasion, writes “…asking people what persuades them to make decisions is not that helpful — primarily because they won't know.”
Behavioural scientist Wesley Schultz has some compelling evidence of why asking people what they think influences their decisions is largely ineffective. In one set of studies, he asked hundreds of homeowners what messages would be most successful at persuading them to make certain changes, such as turning down the heating, recycling more and being more environmentally friendly. Most said that receiving information about their impact on the environment would make them change. However, this made very little difference at all. In another study, people who said that providing them with information about how much money they could save if they reduced consumption led to them to use even more!
Interestingly, the message that most successfully changed their behaviour (information about how neighbours were making changes) was pretty much dismissed as unlikely to have any effect on them at all.