Live to fight another day
There are times when you've done everything right in the sales process and you know what? The prospect simply preferred the other solution. It happens. MOVE ON. No sense overanalyzing why what seemed to be a sure thing, went south.
Source: Michael Pedone, sales trainer
Do a quick review of the steps that were taken and LOOK for areas where you may have been at fault. Most salespeople will only look for what they did right in order to say "See, I did everything the way I was supposed to." If you want to learn from this, in order to reduce the chances of it happening again, it's important to try and identify areas that MAY HAVE caused a misstep that led your prospect to take action with your competitor. Whether mistakes were made or not, don't let a lost deal turn into two, three or four by being hung up on what you can't change.
So, the prospect went with someone else. Take the high road and let them know you will be there for them if things don't go the way they want and back up your words with action. If they are a fish worth chasing, continue to be an occasional presence and offer your industry advice and continue to brand yourself as a trusted industry advisor/subject matter expert so that if your competitor drops the ball, or a new opportunity arises, they give you a second shot.