People then talk with friends, colleagues and trusted advisors. They want to check out whether what is being claimed by the company is actually true. This is the process of word of mouth that intervenes between communication from the company and actual adoption of the product, service or idea. While there are occasional instances of direct influence from company to customer, usually word of mouth is the actual trigger to purchase, unobserved by the company. The most important reason why word of mouth is so effective is the least understood.
Word of mouth is a substitute for experience.
When you speak with someone about his or her use of a product, in effect you are trying out that product indirectly, without taking the risks yourself. So, when a doctor asks a colleague who has extensive experience with a new drug how it has been working out, in effect that doctor is trying out the drug on the other doctor's patients. If the product has been working out in a peer's hands, that is powerful evidence that it will work out in your own hands. I think every business person is aware of the desirability of building positive word of mouth. They ignore it because they think very little can be done about it directly.