When you see that your brethren need help, the Torah says: לֹא תוּכַל לְהִתְעַלֵּם, “…you shall not hide yourself.” (Deut. 22,3) This, Chazal interprets to mean, that you should not look aside as if you do not see what must be done. One must be ever ready to help and cannot look aside.
There is a famous story told about the Chafetz Chaim, the author of the Mishna Berurah. He was once riding in a wagon, as was customary in those days, trying to sell his books. On the way his driver saw a beautiful garden with fruit trees. He could not pass this up so he stopped his horse, climbed down from the wagon. He entered the garden and started to pick some of the enticing fruit.
When the Chafetz Chaim saw this he started hollering, “You are being seen, you are being seen.” The wagon driver immediately dropped the fruit, ran back to the wagon and took off. After travelling a little distance the driver turned to the Chafetz Chaim and protested, “I did not see anyone. No one saw me.” The Chafetz Chaim responded, “You are wrong. You were seen by the One Who sees but is not seen.”
We often think we can do something questionable and no one will be the wiser. We are wrong. We err. Whatever we do has repercussions. We may not realize at first that it will affect anyone else or that we will be found out. But we are wrong. Eventually all becomes known. We know the expression, the walls have ears.