A boy asks his parent whether he can eat a particular chocolate bar. They look at the chocolate bar and say, "I don't think it is kosher."
If the boy then takes the bar, which costs him money, and throws it away, he is showing greatness. His seichel (mind) has overcome his materialism, his money, and his desire for physical gratification.
And so we see that the Torah is a spiritual force that gives us the impetus to be able to fight back against all the urges that make us act only in accordance with own immediate desires. -- Ohr Avigdor Shaar Avodas Elokim