Five points:
"In the light of the day" means after we have examined it further and carefully. It comes from the idea of something being more clearly seen with light shining in it.
"In the cold light of the day" means something similar, but emphasizes that you are examining the situation without emotion.
"It will never see the light of the day" means it will never happen.
You can google the phrases and usually find a good definition.
"Dis-understand" is not a word. Say, "don't understand."