Scott Cook, founder of Intuit says he doesn’t trust what people say in surveys. He trusts what people actually do. When people say in a survey that they would buy a product or do something, there is a 50% chance that they would do it. It’s a coin toss. It’s better, he says, to follow someone who has just done something and ask them why they did it.
Trust behavior (what people actually do), not what people say they would do. Measure behavior and find out why people behaved the way they have done to predict future behavior instead of using what people say they would do (e.g. in a survey) to predict what they would do.
This video is very insightful. Try watching it.