Sentimental Anniversary - S3-E15
Continuity mistake: While Lucy's showing Little Ricky the pictures in the album, we see Lucy's fingernails are not polished, but in the closeup of her hand pointing to the photo the fingernails have dark polish on them. This happens again when Lucy's looking through the album with Ricky.
Answer: There is no reason. It's a just a silly plot device, typical of the era. Women characters were often portrayed as making uninformed assumptions or decisions.
raywest ★