Jesus demonstrated this truth by reminding them that they knew that clouds in the west meant impending rain (from the Mediterranean Sea) and wind from the south (from the Negev desert) meant the temperatures were going to rise. They had the capability to recognize and interpret weather signs.
And they had the capability to recognize and interpret other signs, as well. Only a hypocrite would pretend that he didn't have enough information to know what was just in the circumstances.
Sharon Ringe in her commentary on Luke, points out that:
The social and economic contest for the saying is the rampant debt that was destroying families and communities throughout Palestine. If disputes about debts reached the Roman legal system, one of two verdicts would greet the debtor Either the debtor would be forced into indentured service to work off the debt, or the debtor would be throw into prison until family members managed to scrape together the needed money to pay off the debt (usually by selling off any remaining lands.) It was a system that allowed the rich to get richer, and that spelled the ruin of the poor....In order to avoid playing into such blatant injustice, the only soltuion would be to settle cases before they went to court. Whatever the actual patterns of debt and credit, justice required that the system be brought to an end....