Moshe did not eat, drink or sleep for 40 days when he received the Torah.  The reason could be understood with a parable:

A king once said to his beloved friend, “Gather for yourself gold coins from my treasury.”  In his excitement, the friend did not eat or drink.  Whenever he felt the need to sleep, he said, “If I sleep, I will lose all this treasure!”  

So too, when Moshe was gathering Torah knowledge, he forgot about eating and drinking.  Whenever he felt the need to sleep, he said, “If I sleep, I will lose out, for Hashem has granted me only 40 days!”

~ R’ Chaim Kanievsky zt”l