Welcome to @barmstrong, co-founder and CEO of Coinbase! 

He’s kindly agreed to do an AMA. Reply with your questions. :)

people often comment on your superhuman ability to remain calm under pressure. have you always been that way? or do you cultivate it through deliberate practice? suggestions for building that skill?

...Then repeat. There doesn't seem to be any limit to this as far as I can tell.

Plenty of items that would have stressed me out previously feel totally normal to me now (public speaking, upsetting people with difficult decisions, dealing with crises).

I still get nervous when firing people though - which bugs me.

I think it was partially innate for me, and a touch of aspergers helps. But I definitely feel quite stressed at times, and I think it's a muscle one can build.

Basically, push yourself 20% outside your comfort zone (not 200%) on a regular basis, until that is your new normal...