Principle of commitment & consistency -- When people commit to something, they're far more likely to purchase from you. That's why getting them to agree to something like a free + shipping offer or by agreeing with something you've said in some way. This is a powerful principle in sales and if you pay attention to some of the best marketers in the world, you'll notice that they work fervently to get your commitment to something, even if it's very small in the beginning.
What is a customer funnel
The effort you put into building your email list is one of the best investments you can make online. Having access to the inboxes of targeted prospects means you can continue to build and nurture relationships over time, and become a trusted source of valuable industry knowledge. Then, when it’s time for your prospects to buy, you’ll be the first one who comes to mind.