I posted this as a comment on Nate Jenkins' blog as a response to questions about mental toughness.

i'm not an elite runner (yet) or Nate, but i have some thoughts on the injuries and the mental drive. gone

i had a 2 year stretch of seemingly nonstop alternating injuries; mostly shin splints, plus pain on the side of the knee, and i sprained my ankle once. in that span i became very frustrated and some people might've even stopped running after all those injuries, but i kept going because i knew why i was doing it; i love running and i want to improve and i will not let anything stand in my way. for example, when i had the pain on the side of my knee the 2nd time, i knee it wasn't an injury, but just an ache. i knew it'd go away. in the 3 weeks it took the pain to go away, it would've been easy to say "knee hurts, i'm stopping", but i didn't. i kept going because i knew that i'd be satisfied with what i'd done and that satisfaction heavily outweighs the pain.

also, it may help to have a type of role model for the situation. when i was a freshman, i was friends with the senior captain who had won a state championship in the indoor 600m. during the outdoor season his lower legs got real bad and i think he either got a stress fracture or got very close to one. with the knowledge of that, how could anyone feel right about skipping a workout for a minor ache? how could you see a guy work his legs to fracture, then go and take the easy way out? you might use your teammate, Nate, or anyone else to note this. maybe you'll think of Brett Favre or Cal Ripken Jr. who knows, maybe you don't need to look at anyone but yourself. whatever it takes, if you have an 'injury' that you can train through, then do it. don't let yourself take the easy way out.

about training in NE weather, it's sort of the same deal. I have some hardcore first hand experience in this. i've run in snowstorms with the whole course covered by at least an inch of snow, i've run in a singlet in 20 degree weather, i've run through downpours where there's more water falling down than there is in your shower, i've run when the wind was blowing me over, and i've run in 95 degree heat where i was slowed down by nearly 2 minutes/mile for my 3 mile tempo run. 
you have to remind yourself that you're not out there to enjoy the weather. you're out there to train. you're not out there to enjoy yourself, you're out there to do work. in order to get out in the crappy conditions, you just have to think about why, and what you'd be doing it for. when you're absolutely serious at training and improving, it's easier to get out there. same principle goes for getting out when you don't feel good.

and for racing and training through fatigue/burning/pain/the worst enjoyment of your life:

the drive comes from many different places. for some, it's their coach yelling at them to 'f****** go!". for others, they have to prove something to those who are watching. some find the drive from their desire to win, or beat another runner. some find the drive because they are so focused on their goal time.
some find the drive for the entire race before it even starts; they see it to it's end. when the gun goes off, they are absolutely committed to the task of reaching the finish line.

mantras are probably the most frequently used form. but they'll only work if you find what gets you going. maybe you get too tense or nervous late in the race, and "stay relaxed" is yours. maybe you get too relaxed and "focus" is yours. maybe you lose the drive halfway through the race, and "all the way" is yours. maybe you know you'll feel awful if you dont hit your goal time, so you need to tell yourself "hit the time" over and over. maybe you need "beat him". maybe you're lacking strength, and you'll need to tell yourself to "power through".

personally, i know what disappoints me after a race. i know what i'm out there for. i know if i want to hit a time goal, and i don't, i'll be mad, so during the race i'll wrap my mind around the time, and the effort i know it takes to reach it. maybe my team needs points in the meet so i wrap my mind around beating the other team's runners. maybe i'm facing intense pain, and i need to tell myself to suck it up and stop being a wimp, because i know when i finish, if i haven't given the race my all, i will be disappointed.

getting through injuries, getting into the weather, and getting through the race all depends on giving yourself a reason to do it. if you're stocking shelves for a job, and your boss tells you that if you don't finish the pet food section by 5pm you'll be fired, and you don't care about the job, then at 5:02 the pet food section won't be finished. on the other hand, if you're living your dream job by working in a tall office building in new york city, and your boss asks you to have a report ready for him by the end of the hour, then you're going to make sure you have it done by then.

if you don't actually care about what you do as a runner, then you can't expect to have the drive to do what it takes to become a better athlete. however, if you're certain of what you want to do and what you want to do is be the best runner your body is capable of being, then you should have no trouble finding the will to do what it takes. it comes from within.