In Matthew 18 and Mark 9 it is preceding by teaching about causing children to stumble. There is no necessary reason why the eye-hand account could not have been meant by the Lord to be an independent teaching designed to stand on its own. According to this view Jesus was driving men to see the value of the kingdom and the utter hopelessness of getting in on the basis of their works. While it would be better to enter the kingdom minus something dear to us, there is no amount of self sacrifice which can open the way. Which Block Faith Alcoholism, drug abuse, pornography, and sexual addiction are examples of overt sins which dominate the lives and thinking of millions upon millions today.
People turn to such things because of inner pain.
The sinful addiction provides a temporary distraction. However, it does not eliminate the pain. In fact, it takes more and more of the addictive behavior to keep masking the pain. People can also turn to things like sports, work, home decorating, shopping, recreational activities, and hobbies to distract them from inner pain. These things, morally neutral in moderation, can so dominate a person's time and attention as to become idolatrous and sinful.