For the non-pilots who have an interest in this;
It's hard to explain to the uninitiated just how differently an aircraft flies when near the top of it's operating envelope compared to just a few thousand feet lower, and what these degradations and thin margins mean. If you're near the top end of that envelope, even something as little as a unforecast, sudden rise in temperatures aloft of 5 to 10 degrees can require immediate action (descent to a lower altitude because engine thrust isn't available in excess at altitude) because the top of the envelope is lowering...crashing down if the temp rise is quick enough.
Thanks AMF. For SLF such as me , this discussion is a fascinating eye-opener regarding the rationale behind these various parameters of high altitude, temperature change, weight, thrust ,AOA etc.