We would all answer SIN! But which sins causes us to react? The sins that we are doing, that we enjoy, and that we are reminded of. In other words, we all would agree that sin is bad. Yes, Amen, right on! And you would say, "Yes, that and this sin is really bad. What a shame that people are doing that sin! But then a sin is mentioned that you are doing, and guess what, we suddenly get offended. The reason is that you and I want to cling to the sins that are really a part of us. We don't want to change.
But the apostle Paul says we are to examine ourselves. He writes: "But examine everything carefully; hold fast to that which is good" (1 Thess. 5:21). See also: (1 Cor. 4:3; 11:28; 2 Cor. 13:5; Gal. 6:4)
One of the Greek words for exam is "dokimazo" and another is "peirazo." They both carry the thought to try, to test, to prove whether one is acceptable under testing. "Peirazo" carries the thought of "to try whether a thing is genuine or not, or whether it can be done!" We are to examine ourselves as to whether we are the genuine article or not! We all have those things in us that are not correct though we don't want to admit our failings. Can we face the truth? Can we confess that in all things we have belief issues that are all fouled up? If someone points those issues out, how do we respond? Generally, defensively. We have to be ready to say, "that is a sin inside of me that I have to 'fess up' to."