We make most of our decisions at a subconscious level, which means, by definition, the operations of the decision process are inaccessible to our conscious minds.
Asking people if they intend to buy something is analogous to asking them if they intend to go to the gym – the results may not correspond well with future behavior. Context is a vital driver of behavior.
Forcing people to consider something rationally that operates on an unconscious, emotional level, is always going to give the wrong answer.
Market research can be useful or interesting to understand what people think they think, but the data it gives shouldn’t be understood as ‘true’. It needs to be interpreted, triangulating insights from as many sources as possible.