Unpublished Sense Puzzle

How to fit 5 squares into a defined and imposed surface? 
The challenge seems very simple but turns out to be a formidable challenge. 
Each piece is adjusted to the tenth of a millimeter and very quickly gives the illusion that it is impossible to fit the 5 brackets into the frame. 
Looking at this puzzle, we get the impression that it is not complicated and we are far from imagining that it requires formidable insight and enormous patience to find the solution.