The true saying "What is written without effort is in general read without pleasure" is usually attributed to Samuel Johnson.
Well, most things like this seem to be attributed to Johnson, Churchill, Einstein or Twain.
Quote Investigator is a wonderful website for people who are suspicious of loose attributions. They think Samuel Johnson did use a similar expression ('What is easy is seldom excellent') but there are many precedents.
I could have done with them when we started the Simplification Centre. I collected quotes on simplification, including 'Einstein's' saying 'Everything should be made as simple as possible, but no simpler'. I assumed he probably hadn't said it but couldn't find any evidence either way.
It turns out this attribution is a pretty good one, although it is a summary of something Einstein said. Quote Investigator concludes:
'...Einstein may have crafted this aphorism, but there is no direct evidence in his writings. He did express a similar idea in a lecture but not concisely. [Composer] Roger Sessions was a key figure in the propagation of the saying. In fact, he may have crafted it when he attempted to paraphrase an idea imparted by Einstein.'