Originally a red thread was tied to the outside of the door of the Ulam on Yom Kippur. If the thread went white, it symbolised that the people’s sins had been forgiven and vice versa. Later the thread was tied to the inside of the door.
The gemoro Yoma 67a states that Chachomim stopped tying the red thread there in case people would see inside and be upset and ashamed if it had not turned white.
My question is what would be so bad if they were upset and ashamed? If their sins were not forgiven, surely the appropriate reaction is to be distressed?
A possible answer might be that since depression, upset or sadness is such a negative emotion it is better that the people do not know whether or not they have been forgiven. Is there any support for this idea or a better one?