I don’t think this is true. I personally think of it as “going sicko mode”, and it’s the difference between writing as fast as I can for 2 hours straight during an exam, and putting in half as much effort during an entire work day. I can think way harder under pressure. One of the most influential things anyone ever said to me was pointing out how much slower I am during normal work than a high pressure situation. I could write 1000 words in the time between waking up and getting out of bed if I could go sicko mode at will.