What the eye doesn’t see the heart doesn’t grieve over

We are not worried by things that go on without our knowledge. For example, if the chef in a restaurant makes a practice of spitting in the frying-pan to make sure the temperature is right for the Crepes Suzette, the diners are not distressed, since they do not see it happen.

See also:

• Where ignorance is bliss, 'tis folly to be wise