“You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart."
Matthew 5:27, 28

Let's consider this: According to the Kinsey Institute's FAQ, "54% of men think about sex every day or several times a day, 43% a few times per month or a few times per week, and 4% less than once a month." So let's average that out to a very conservative estimate of twenty sexual thoughts per month. That's just one lustful thought every day or two. If we assume that these thoughts begin around puberty, for most men around 11 or 12, then by the time a man has reached the median age of 35 years, he will have, according to Jesus, committed adultery in his heart no less than 5,640 times.

Now, let's give him a break, shall we? Let's assume he got married at 27, the median age, and his thoughts from that point on were only for his wife. He never had another lustful thought apart from his bride. At 27 years, he still will have accumulated 3,720 commissions of heart adultery. Frankly, that's not that much better.

What about women? Most would agree that women think about sex less than men. So let's again take a very conservative estimate of once every 4 or 5 days. At 35 years, our average woman has accumulated 2,000 commissions of heart adultery. If she also attains purity of thought at marriage, around 25, she still has 1,200 commissions of heart adultery. Sure that numbers really been whittled down, but how well would you fare in a court of law with 1,200 guilty charges against you?

Now how's that "little" sin looking? And that's just one of the Commandments from our holy and just Creator.