I’m assembling a big report for MSHA in LaTeX and using the book document class, which normally justifies just splendidly. So when it stopped justifying paragraphs correctly and was giving ragged right edges, that was a problem.
Long story short: I copied some different environments (description, etc) from the web and brought in a \flushleft, which I thought would just apply to that element. Wrong. It changed the setting from then on. Removed all the \flushlefts, and it sets the paragraphs correctly.
And hurray for science and methodical debugging…..”Well the first section is right, and the beginning of section two, and then it goes to shit after this list here. Hey, what’s this \flushleft doing here?”