Lucy Has Her Eyes Examined - S3-E10
Other mistake: When the eye doctor has Lucy repeat the same letters on the eye chart that she claims Ricky got all wrong, she repeats the same letters out loud, then moves closer to the eye chart and repeats the same letters out loud, then pauses in error when she read them all off correctly: P E C F D.
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 ★