More often than not, these lost sales hurt the most because you do not have enough going on. The best answer to this predicament is MORE PROSPECTING. If you had three sales you were attempting to close that week and got one, the two that got away would not be painful.
As for analyzing what went wrong, this is only good energy if you immediately apply what you learned. Sometimes the answer seems confusing and is really very basic ... so I will leave you with this;
Too often the sale is lost because we did not ask for the business! Did you try to close? No? Maybe the other sales person did and that was the only difference!
Don't stop at the presentation, try on a close (this only works if you are dealing with the buyer - that person authorized to make the purchase. If you are not then you shouldn't be spending a lot of time on this account!). I hope this helps.