I’ve been drinking diet mountain dew and diet dr. pepper for so long, I don’t notice the difference in taste of the artificial sweetener from real sugar any more. Sometimes when I order at a restaurant, I wonder if they messed up and gave me the “real thing” instead of the diet version. The only way I can tell the difference is to taste the sugary version and immediately taste the artificial version. Only then do I notice the slight “off” taste.
Similarly, the contrary doctrines of demons and traditions of men often feel very good and can be very close to the “real thing”. If they were too different, it would alert people to that difference and they would abandon the false teachings. The enemy often comes in the guise of an angel of light (2 Cor 11:14) tickling our ears with things we want to hear (2 Tim 4:3).
Even a little “off” should trigger alarms. All it takes is a little leaven to leaven the whole lump (1 Cor 5:6).
We are advised to “prove all things, and hold fast to that which is true” (1 Thess 5:21). We cannot base our “sense” of the truth on feelings. The only way we can prove something is to have something to measure against as a basis for comparison.
Scripture is that basis, and is our measure for all truth (2 Tim 3:16). The only way we can spot the falsehood is to be well grounded in that truth. Test all doctrines (teachings) and beliefs against the standard God has given us in the Bible.