In The Perfect Salesforce, Derek Gatehouse has done a good job of quantifying what makes a salesperson great, and how to hire and coach sales talent based on their sales stage : Not every salesperson is skilled at both "opening the door" and "closing the sale" for a complex sales cycles.
"Door openers" often have plenty of deals in the pipeline forecasted at 10% and 20%, but may not have the skills to realistically qualify a deal and make the committee sale to drive it to closure. Conversely, seasoned closers are generally not the right salespeople to generate new business, because they deal in quality, not quantity. It takes a staggering volume of outbound "cold" calls to get a potential prospect on the line -- and top salespeople know that to optimize their time, they need to focus on deals that have the greatest potential of closing.
There's a reason that so many telesales firms are staffed with great "openers" (who often moved from direct sales to inside sales once the sales process became protracted), and so many direct sales teams are staffed with great "closers". But neither functions can stand alone.
Matching the right openers with the right closers ensures that you'll have sales people in place to make goal (and a support team to make the assists).