We make use of the metaphor of a sales funnel (wide at the very top, narrow at the end) to monitor the sales process. Towards the top of this funnel you've got 'unqualified prospects' - the people who you believe may need your service or product, but to whom you've never spoken. At the end of this funnel, many delivery and sales steps after, you've got those who've received the service or product and have also purchased it. The metaphor of a funnel can be utilized because prospects drop out of different stages of an extended sales process. Using the sales funnel, and by calculating the amount of leads at every point of the procedure, you are able to predict the amount of prospects who'll, over time, become clients. A lot more than this, by taking a look at how these amounts change with time, you are able to spot issues in the sales pipeline and just take corrective action early.