Bad design

Bad design is attributed to games that have Gameplay artifacts that unfairly punish the player should they not do as the game orders of them.
Bad design can also be exacerbated by games punishing players simply because they didn't know any better.

Terraria's boulder trap removes up to 400 HP instantly despite the fact players are not allowed to see it; A crystal-clear example of bad design.

Furthermore, they are not made aware of its existence until much later on in the game, meaning if they've attained valuable items it's all lost in a matter of seconds without the chance of retaliation.