Good thoughts so far Brute.
I think 'Mental Strength' has a very interesting relationship with 'Goal Setting'. They are a very synergistic pair of factors.
1) With a high degree of mental strength but no actual direction or concrete goal even the most mentally strongest trainee may well flounder. One can often see this with trainees who have never or never recently been taken out of their comfort zone. I hope BtB doesn't mind me saying that although I believe he has a good degree of mental strength, his mindset prior to our training experiment was not one of pushing himself for certain goals. He has become much more goal orientated and as a result that has had a synergistically positive effect on his mental strength and has benefited greatly his results.
2) Just as unproductive can be a high degree of goal setting but without the necessary mental strength to execute through the plan. This is often categorised by people who set goals but 'lack follow through'. I think this is probably more common that the above scenario but both are equally unproductive.
Just a few thoughts, I think this is one area which is massively important but actually pinning it down and categorising what it actually is, is quite difficult. Something like 'having heart' or 'commitment' or 'how bad d'ya want it' are probably all true to some degree but not necessarily accurate and mean different things to different people. I'll write more later.