I like what runningart2004 is saying... Preparation is everything... Without proper preparation, you will not be there at the finish. I find Webb very interesting, talented enough to have a chance of winning on any stage, yet missing to a large degree the confidence, know-how, and poise to maximize his obvious physical potential.
I think it is a waste of time trying to dig into his head looking for the answer, some people just have the killer instinct, the natural feel of how a race flows, and he is not one of those people AT THIS TIME. Whether it can be learned or developed I don't know, I'm not a psychologist. There are some basic tactical scenarios in 1500 running, and I think all that can be done for him on this front is to study all potential scenarios known, and devise plans for dealing with whatever scenario(s) present themselves on the day. So much happens so fast in the 1500 however, that even the best runners can be shut-down by simply how the race flows, regardless of how well laid out their plans may be. So I think outside of studying some standard scenarios, there is not much more that can be done for him mentally / tactically.
What can be done is giving him the best "engine" to go out and race with. When you are physically prepared to WIN, tactical scenarios can be dealt with much easier, since they won't exhaust you as much. If you are not tired with 100 to go, you can kick like a friggin lunatic. The biggest controllable variable is being in top physical condition, and this is what has to be focussed on. Not sprinting ability, not tactical awareness, just BEING AS PHYSICALLY READY AS POSSIBLE TO RUN 1500 METRES AS FAST AS POSSIBLE, AFTER TWO NEAR MAXIMUM EFFORTS BEFOREHAND. You can run the race any way you want then! El Guerrouj's 1500 win in Athens was something to witness, the guy went out easy, GRADUALLY strolled into the lead not burning up too much of his reserves, then hammered the crap out of everyone in the last two laps with the mindset of, "I am the fittest athlete, stay with me if you can, but I bet you can't". Where were the big kickers then? Left in the dust... Silva had a heck of a last lap, but El Guerrouj burried him and his 50 second closer the lap before... I read somewhere that preparation is #1, #2, #3, and when you get to #97 we'll talk about psychology.
The real question is, how do you properly prepare an athlete for two near-maximal efforts, followed by one maximal effort all in just a matter of days? Given Webb's difficulties and seeming confidence issues, he has to be given the fastest ride to win. Amazing how confidence incrases ten-fold when you know you are fully prepared to beat anyone. The other stuff has a much greater chance of falling into place then. I wish him well, he certainly is interesting to watch.