Would you buy a vacuum sweeper from a door-to-door salesman? Probably not. In the first place, you don’t want someone bothering you at your house. Additionally, you don’t know him or trust him. The same can be said about evangelism.
It is expecting a lot for a person to listen to a stranger… especially with something as important as religion. They don’t know you and they don’t trust you. Once in a while, there is an individual who will open up to someone they have never met and talk about deep personal issues… but that is the exception. We should continue evangelizing strangers but realize that it is unlikely they will be all that receptive. There are so many charlatans and scammers out there today that there is a high level of cynicism.
This means we need to work hard at building relationships with non-Christians. Until they know and trust you, they will be less likely to listen to you.