As a body/mind experiment the Israeli army sent four groups of soldiers on a 25 mile forced march. Group One was told exactly how far they were to go and were kept informed on their progress. Group Two received no information about how far they had gone, nor how far they had to march. Group Three knew it was a 25 mile march, but, at the last moment, were told they had to go further. Group Four was told they had to march 50 miles, but were stopped when they got to 25. The outcome was that, even though they all ended up doing exactly the same thing, only those who knew exactly what they had to do and where they were up to came out of it relatively unstressed.
It reminds us that our greatest source of strength is a calm mind that knows where it is going.