These things happened to them as examples and were written down as warnings for us, on whom the culmination of the ages has come. 12 So, if you think you are standing firm, be careful that you don’t fall! (I Corinthians 10:11-12 NIV)
It has been my observation in life that many seemingly strong Christians seem to have severe spiritual failings later on in life. I suspect that one cause of this phenomenon is over confidence. They are so used to being successful that they forget where their success came from. It did not come from themselves, but from God. Those of us who are Christians should never become arrogant because of our presumed spiritual successes. We should remain humble, inspect ourselves for error, and pray to God daily to keep us from failing.