Who says sinning is still an option for the Christian?

In Romans 6, the Apostle Paul writes that we are not to "offer the parts of [our] body to sin" but we are instead to "count [ourselves] dead to sin."

So, why then do we continue to act as though sinning is still an option to us?

Psalm 111:10 says that, "The fear of the Lord is the beginning of wisdom."  In this instance, that means that we would be wise to take what Paul says in Romans 6 as a commandment, instead of as a mere suggestion, which we so often do.