Discernment

The great tribulation will reveal who is able to persevere in faithfulness to God when challenged by the lies of Satan. The level of deception achieved by the man of sin will be so high that unless a person has had their spiritual senses trained to discern good from evil, they will be deceived by his lies.

The single most important aspect to remember about the return of Christ is that everyone will see it for themselves. No one will have to be informed. If you haven't see it for yourself, it hasn't happened, regardless of what anyone says. Jesus cautioned specifically about this.
So if they say to you, ‘Behold, He is in the wilderness,’ do not go out, or, ‘Behold, He is in the inner rooms,’ do not believe them. For just as the lightning comes from the east and flashes even to the west, so will the coming of the Son of Man be. Matthew 24:26-27

BEHOLD, HE IS COMING WITH THE CLOUDS, and every eye will see Him. Revelation 1:7a
The man of sin will not be perceived as evil by most of the world. Most will see him as a savior, and in a sense, they are correct since he did restore order to a world in chaos by using supernatural power. This will be a very strong delusion and only those with spiritual discernment will be able to see through his ruse when he claims to be God and demands worship. The worship he will require won't be merely lip service or some humbling gesture, although that may be part of it. He will require obedience to a code of conduct that affirms his claim as God and ruler of the world.