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Sorry but I'm not familiar with this 
Briefly, off topic, my pal came from Perth. He told me that sometimes a monkey might go up a tree to find food, stick its paw into a hole in the tree to fumble for grub, and then find he could not withdraw the paw. In panic,the monkey's paw stayed in place in the hole, bcs the monkey did not stay cool and figure out how to withdraw its arm from the hole..... which eventually led to death
In UK, we might say,'when in a hole, stop digging', but it is not quite the same thing.
tl:dr 'Mental monkey grip' means being flexible, not making bad decisions in adversity, and not repeating the same actions, if they are not succeeding. It only drives you deeeper and deeper into the same crevice,from which there is no return. This can be particularly applicable to gameplay, but has some application on the forums also
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