It's a shame to pursue a sales lead and then not only lose the deal, but not learn much from the experience, either. Gaining wisdom from win/loss outcomes is apparently an overlooked practice. It was the lowest-scoring metric in the sales process, according to a recent study on sales performance optimization.
The vast majority of companies -- eight in ten -- rated their win/loss intelligence as average, poor, or even "dismal". From the same study, salespeople are typically making multiple calls over the course of weeks if not months, trying to close deals, but only winning half the deals forecasted. This is like paying tuition at the "school of hard knocks". Sales leaders would do well then, to learn more about why bids are won or lost.
Brief surveys with customers can be productive in this regard, combined with internal debriefing among sales team members to sort out the useful facts from pursuing the opportunity. The "money" facts are learning the main reasons for the outcome. But it's also helpful knowing the type of solution being pitched, customer business issue, size of the deal, upside potential, etc. Use the results to adjust who you target, how you screen leads and other changes to your sales process and communications.
The main challenge in retrieving win/loss data? Salespeople instinctively put deals behind them and move on to the next ones, rather than dwell on post-mortems. Consider a process requiring just a limited amount of time from salespeople. Help them see the reward in debriefing each deal, including learning more from their colleagues' ideas and mistakes.