Have you ever come home with a new product or service and wondered why you bought it? Was it a spur of the moment thing, a need you did not know was there until you saw the product or maybe a great discount or commercial dress you in?
What do you tell yourself about such a buy later? Do you rationalize it?

Go and experience
Finding out what triggers a sale can be extremely challenging. One way to go about this is to follow customers as they are making decisions in their customer journey. Before interpretation you need to go and see, be like an anthropologist on a research project. Try to walk a day in their shoes and empathize. This will give you immediate feedback on what makes a customer decide something. It does not yet tell you why he decides this, but this is ok. For now just watch and learn. You can do this with online and offline sales.
- See whether they were consciously looking for your product
- See what kind of input makes them act more or less secure
- See what delights or irritates them. Are there things slowing them down?
- See what does neither delight or irritate
- See what makes them delay or speed up the process. Do they want more or less features? Do they look at price?
- See if interaction with other people make a difference
- See at what point they decide for you and buy, are there competitors in sight? Do they buy other stuff at the same time?
- See if they buy it when alone or together
There is much to discover and learn. It is important to have observations before you start asking for motivations. People do not always have a clear insight in why they do what they do.
Consumers don't think how they feel. They don't say what they think and they don't do what they say.