Terribly sorry sir, but you're not supposed to be here

[Jinix]

Game designers must allow for this. If there is a way to climb over, under or jump to a forbidden place - gamers will find it.

I hopped and climbed on everything looking for more things and piling boxes to climb up somewhere is an old Thief habit that dies hard and when you see pickupable boxes laying around you think stack and climb to unreachable places for more goodies.
But this isn't that sort of game.
In Thief I remember spending whole evenings messing around with boxes trying to get high enough to reach a wall or roof, only in that game they would break after two or three handlings and more boxes were in short supply.