You do a ton of marketing with the aim of getting sales. A sales funnel is the process that moves people from someone who has never heard of you, to your landing the sale. Instead of just randomly doing marketing, the sales funnel is something that you set up to ensure that no one gets lost along the way.
Losing sales by mistake happens when someone is interested in your product, but forgets about you. Your funnel needs to be set up in a way that makes sure they have to make a conscious decision, whether that is yes, or no on whether you are the right wedding business for them, and if so to sign a contract, or buy from you. For more details on a sales funnel make sure to read the article by Stacie Francombe of Inspire Smart Success!