How Can Jesus Come As a Thief in the Night in the Post-Trib Teaching?

1 Thessalonians 5 does speak of the Lord returning as a thief in the night. However if you will read that chapter you will learn that it only applies to those who are in darkness. 1 Thessalonians 5:4 says, “But ye, brethren, are not in darkness, that that day should overtake you as a thief.” So according to this verse those of us who are children of light should not be caught off guard by the day of the Lord.