A Suspicious Black Chest | Paper Mario: The Thousand-Year Door OST 

What I find particularly amusing is actually that they *don’t* keep falling for the curses. They fall for maybe the first two, but by the fourth they’re just done and immediately call the chest on it. That whole conversation and curse sequence is gold.

Because they are tricking the chests so they give them powers

More like: why do the guys think they're cursing them when they aren't? These "curses" are clearly beneficial

@@skullplasma0221 I think it's more that the curses are sort of considered arcane techniques in the context of TTYD. They're forcing a shameful technique on Mario, even if it is beneficial.

@@coutamaxplayer538 The chests contain the spirits of the original heroes. They are willingly giving Mario the powers but are disguising them as 'curses' for whatever reason.