Worrying does not empty tomorrow of its troubles; it empties today of its strength.
This quote not only came with the ubiquitously American comma splice, but also it's before trouble and strength. I always see red over errors like that.
While reading some materials relating to British publishing, I found a telling statement that in the UK, two sentences were joined with a semicolon, but that America now used a comma almost exclusively. The way it was worded made it clear that even educated people in America did not know how to use a simple semicolon properly, and the world had given up on changing their minds, as if they really didn't have one.
It's = it is. How hard is it to imagine saying "it is trouble" or "it is strength" in that sentence? A native speaker's ear will quickly set them right.