The goal of modern marketing is not to make an immediate sale, but to find people who are interested in what you do.  When your leads respond, you can ask them if they would like to purchase, otherwise you continue to build a relationship with them based on trust.  This will establish you as an authority for your product or service.  

The truth is the vast majority of people are not going to be ready to make a purchase on the day they see your ad.  If you don’t collect their contact information and follow up with them - the majority of your advertising money is wasted.  If they are ready to purchase 6 months later - the chance is they will not remember you unless you have messaged them in the meantime with something that offered value to them.