One question is why he would die if he lifts up the wrong box. The minotaur is said to only come out if he cheats. So one possibility is that there's some kind of evil or danger (e.g. electricity) under six of the boxes. Alternatively he will damage the tool(s) if he doesn't lift the right box. For example, a map may be torn, burn or taken by the wind. If the boxes are the tools, he may break some boxes or the arrangement of the boxes. Another possibility is that he gets stuck on a box and can't get up or down, or that all the boxes fall down on him and kill him.