This Chinese proverb is used in situations where you cannot explain someone's behaviour or times when anything else is tough to work out. It is very similiar in use to the English proverb "Unable to make head or tail of it". This proverbs translation, therefore could be much more simple in its ability to describe something that you are unable to explain. Such as 'inexplicable' or an 'unfathomable mystery'. I personally like the full translation though.
mò míngqí miào
No one can explain the mystery (wonder) of it all