In reply to IainRUK: For me that's what "hard" is. Not the race, but putting the training in. The mental strength to go out when you don't want to for whatever reason.
I find it helps to remind myself how much worse it feels to lose fitness/sharpness and how hard/depressing it is until you get it back (or start getting it back). All you need to do is miss the odd run here and there through working late, busy with the kids, tiredness etc., and then suddenly the consistency in training has gone and bye-bye fitness.
I was genuinely shocked at how a lack of consistency and focus in my training dramatically effected speed and endurance. I thought I was at least maintaining fitness during that time (I've two young children and have been struggling to re-organise the training regime as I can't run at the same times/have the same rest days etc. as before).
Running became almost unenjoyable as I kept trying to go as fast as I used to but couldn't. Consequently, I overtrained, was always heavy-legged and lost motivation, thinking maybe it was my age or I'd reached my limits somehow. Now I think I've (almost) accepted my current state and can build up again more sensibly and just be patient for the results, which are starting to come (slowly).
For me that was the "hard" part. Harder than actually running a marathonm or any event - which is only really hard if you haven't trained properly and, even then, is over in minutes (or a few hours) whereas training/motivation issues can last much longer.
There might be a reasonable amount of grit and determination required to finish some races if training and/or pacing in the race itself was not ideal for the conditions and I guess the amount of digging in you are prepared to do could be considered as hardness, but I've only ever experienced physical issues except perhaps in my first marathon where I battled for 6 miles with the urge to stop and walk! Now I undertand this feeling more, and am better trained, it's not an issue.
On 10Ks I tend to feel like my insides are going to explode out of me or I will collapse as my legs turn to jelly, but I consider that to be more of a physical battle of pushing on just under that threshold! Whether somebody else could push harder or not and still get away with it I've no idea - so hardness in that sense is relative and I'd never know what discomfort somebody else was experiencing or what my physical limit really was (until I surpassed it for myself and actually had an "accident" or fell over). Perhaps top athletes understand their bodies much better and know where the limits are (and of course have also done loads of training).