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.
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:

“Favorite rejoinder of Senator Harry S. Truman, when a member of his war contracts investigating committee objects to his strenuous pace: ‘If you don’t like the heat, get out of the kitchen’.”