If you can't stand the heat...
If you can't stand the heat, get out of the kitchen. Don't persist with a task if the pressure of it is too much for you. The implication being that, if you can't cope, you should leave the work to someone who can.
From one plain speaker to another... We're Wild About Harry now more than ever before.
This is widely reported as being coined by US President Harry S. Truman. That's almost correct, but in fact, Truman was known to have used it at least as early as 1942 - before becoming president. Here's a citation from an Idaho newspaper The Soda Springs Sun, from July that year: