The book of Hebrews is somewhat infamous for its warnings against falling away and willful sin. Hebrews 6:4-6 says that for those who have been enlightened (and so forth) and yet fall away, it is impossible to restore them again. And Hebrews 10:26-31 says there is no sacrifice for willful sin, and it promises vengeance against those who count the blood of the covenant a common, unholy thing.
But chapter 2 shows the beginning of the path that leads to that fiery end. The verses here do not speak of outright rejection, but rather of drifting and neglect. It is a subtle process that involves regularly prioritizing things of lesser importance above the opportunity that has been opened to us. In time, and with a continual focus on lesser things, faith begins to wane and one's spiritual strength is sapped. A callous forms on the heart, such that God's word can no longer get through.
The falling away and willful sin, then, are the late-stage result of a person routinely prioritizing something - anything - above God and His message. Through his or her own training, the person becomes essentially unable to make the right choices, and willful sin is the result. The heart becomes so calloused that it no longer cares what God says or thinks. But it begins with drifting and neglect.