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sitzfleisch: the ability to endure or carry on with an activity

Something Oppenheimer did not have, apparently.

loaned from German, where it's originally a way to say buttocks, literally "sitting flesh". If you have more Sitzfleisch you can sit for longer. Both in the literal sense (a bigger butt makes sitting more comfortable) and in the figurative sense (having the mental ability to sit for longer, get more desk work done)

I think there is an IT bit of humor from about 1 decade+ back where the people who's proposals won out in meeting were the ones that could keep from needing to go to the bathroom longer.

Fascinating crossover from literal to figurative that you find so often when you trace language back far enough.

Don’t worry, the link provided by the GP did nothing to explain what was meant anyway.