I've spent some time wondering about this passage also, and will share my current exegesis, without trying to say any other answer is wrong. There may be many interpretations of this dense passage.
First, let's understand the background.
The Church in Thessalonia was worried that the Day of the Lord had already come, and they were left behind (yes, like Nicolas Cage). So what Paul is describing to the Thessalonians is how they know they have not been left behind, and this does not necessarily contradict the notion that the day of the Lord will come without warning, although there was general expectation of apostasy in the latter days (e.g. 2 Peter 3.3) but such a situation is sufficiently vague that it does not provide practical warning as to the specific time of the Lord's return, and thus the notion of Christ coming as a "thief in the night" is still a message of coming unexpectedly and so still can create panic that you've been left behind.
Do not let anyone deceive you in any way, for that day will not come
unless the rebellion comes first, and the man of lawlessness is
revealed, the son of destruction, who opposes and who exalts himself
over every so-called god or object of worship, so that he sits down in
the temple of God, proclaiming that he himself is God. Do you not
remember that while we were still with you, we were saying these
things to you? And you know that which restrains him now, so that he
will be revealed in his own time. For the mystery of lawlessness is
at work already; only the one who now restrains will do so until he is
out of the way, and then the lawless one will be revealed, whom the
Lord Jesus will slay with the breath of his mouth, and wipe out by the
appearance of his coming
In order to try to understand the "Man of Lawlessness", let's first think about the "mystery of lawlessness". We know
It is already in the world and was at the time of the Thessalonians, so it is not a person but rather a spirit, or force, or philosophy
It is being restrained, but the restrainer will be taken away.
Now there are two popular interpretations for "the restrainer", either the church or the Holy Spirit. I favor the Holy Spirit as a spiritual restrainer for the spiritual force of lawlessness (and also if it was the church, then the Thessalonians would view themselves as the restrainer, and this passage and their concerns wouldn't make sense).
We know that the Holy Spirit was poured out on man on the day of Pentecost, and this passage is suggesting that before Christ comes back, that Spirit will be removed, thus no longer restraining the mystery of lawlessness, allowing the mystery of lawlessness to become the "man of lawlessness".
If we accept this association for the restrainer, then we have a ready interpretation for the son of destruction:
the man of lawlessness is revealed, the son of destruction, who
opposes and who exalts himself over every so-called god or object of
worship, so that he sits down in the temple of God, proclaiming that
he himself is God.
Of course we are each the Temple of God, it is not a building made with human hands. Within that temple, the holy spirit is a witness testifying to us and convicting us, but when that witness is removed -- think of humanity with no conscience or restraining force, no "inner voice" crying out to convict us. That leads to man completely believing he is God, with no nagging conscience or fear. This, to me, is the definition of "man of lawlessness".
Thus when the day of the Lord comes, the Spirit will return to the Father, along with the saints who will meet him in the air, and Christ will come in glory and splendor, destroying those still left on earth by the splendor of his coming. Those still left on the earth are those that God gave over to a "powerful delusion" because they didn't love the truth, and without the Holy Spirit to convict them, there is no possibility of breaking out of that delusion. The delusion is that man is God -- which is the essence of lawlessness.
This is something the Thessalonians would notice. They do not view themselves as God. They know the Holy Spirit is still in them. So they don't need to worry that they have been left behind.