Mental endurance or mental strength?

I had a pretty difficult week at work. As a result I only trained once - Thursday night when I went swimming. I was surprised at my reaction, because I never allow myself to 'give in' to circumstances. That does not mean that I am immune to negative events or circumstance, but I try not to be swayed by them, and see them as the obstacles that they are - simply obstacles. I think that I am quite adept at compartmentalising my work life from my personal life, and this is quite helpful in keeping me focused on what is really important in my life - my family. Challenges are only challenges because you THINK you cannot overcome them, has always been my philosophy. Admittedly I have not always understood what that means, but I think I may have finally worked something out!
Things have been rolling along nicely with the tri training in general. I have cut down on the running, and do not race on Sundays anymore, as I am trying to develop my cycling and swimming skills. I usually look forward to my sessions and often manage to run in the mornings, and either swim or bike in the afternoons. Mind you, I use the stationery bike, as proper rides are reserved for weekends when I have more time.
Given all of the above, when I think about mental strength, I first thought it meant having the determination to set and see through your goals. In this case, the training was necessary, and getting to each session was a necessary step to achieve the bigger goal or a race or a tri. My week at work has made me think a bit more about what this means, and how this translates into my tri training.  All desire to train vanished this week, and I felt a bit tired mentally.  Logically I was able to understand what was happening at work, as just that - processes which I was unable to control.  Yet I allowed myself to become mentally fatigued.  It also made me wonder about whether I need to develop more mental strength or endurance.
The Oxford English dictionary defines Endurance as "the fact or power of enduring an unpleasant or difficult process or situation without giving way" whilst Strength is defined as "the emotional or mental qualities necessary in dealing with situations or events that are distressing or difficult".   I think that I was able to understand and deal with the issues at work in a way which makes me think that I am clear on the mental strength side.  Endurance though, seems to be another story.

Historically 'endurance' has always been associated with martyrs and saints (who have endured endless suffering and torture).  The other context has been associated with women, slaves, the poor etc who have 'endured'  all kinds of horrors.  True, they may have overcome in the end, but meanings associated with 'endurance' seem to suggest a kind of passive acceptance, of holding on through thick and thicker.

I understand that this is a more complex issue than that which I am focussing on, but 'endurance' has not been one of my favourite things.  Strength has positive connotations which somehow endurance has not quite managed yet.  Whilst it is also true that words can become pejorative over time ('sods' no longer refer to the earth, but to unpleasant beings) or completely change their meanings ('gay' is rarely used to indicate happiness, 'booty' is no longer a pirate's stash of gold).  Why am I telling you all this?  Well maybe 'endurance' means something a bit more than enduring ultra distances, unpleasant people or difficult situations. 

In thinking a bit more about mental endurance, I think the key lies in the second part of the definition "the power of enduring....without giving way".  I am not sure if I would interpret that as blindly sallying forth even under difficult circumstances, getting the training in even if it is not of a good quality.  But this week I realised that mental endurance is an aspect of triathlon training that needs to be developed along with bike technique, faster swim times and more powerful runs.  How exactly I set out to do this, is the topic for another post.