What does "hard to know," mean?

"It would be hard to know", might mean it is a complicated question or I don't have enough information to be certain. A person who is "hard to know" may be shy, secretive, introverted, have social anxiety or other ways in which they do not reveal very much information about them selves for what ever reason.

It depends on the context. An example would by "Why did he kiss her?" "Hard to know" means I have no idea or I have no clue. However, another example would be "How wide is the universe?" "Hard to know" would mean that scientists do not have a way to determine. So it is either a personal "no idea" or a factual "there is no way to determine".

I think it means 'Hard to say really' just in different wording :D

Difficult to understand.

http://www.merkle.com/brainLimits.html

http://www.scientificamerican.com/article/the-limi...