Why was there real-life tension between actresses Mary Tyler Moore (Laura) and Rose Marie (Sally)?

Originally, the series was intended to focus primarily on Rob's office life, with Sally Rogers as the female lead and Laura Petrie as a minor character. However, Mary Tyler Moore's portrayal of Laura became so popular that the producers shifted course to focus more on Rob's home life. Even Rob's office scenes often involved Laura in some way. While the actresses were not openly hostile, Rose Marie's dissatisfaction was well-known.

Asked by Susanna Henke · Last updated 5 years ago · 6.4K views · SOURCE