Know that for the human mind there are certain objects of perception which are within the scope of its nature and capacity; on the other hand, there are, amongst things which actually exist, certain objects which the mind can in no way and by no means grasp: the gates of perception are closed against it.
MaimonidesThe business conduct of the disciples of wise men is truthful and faithful.... He does not allow himself to be made a surety or a guarantor and does not accept the power of attorney.... He lends money and is gracious. He shall not take away business from his fellow man.
Maimonides