[Fit]

Final Hint - what was Lord Voldermort's mistake with his 6th Horcrux...?

The boss was over confident in the subordinate with a simple instruction to mount the signage. He did not check back whether his instruction was understood correctly. He could have said "fix it at six feet' and the subordinate understood it as 'fix it at six feet above". That was how the signage was up there!