In Guardians of the Galaxy, Quill only survives holding the Power Stone because he has Celestial blood.
In Avengers: Endgame, Hulk uses the Infinity Gauntlet absorbing the intense gamma radiation because he can, but he suffers severe damage (which that alone is a post - why? He was "designed" to absorb gamma and supposedly no upper limit to the amount of power he can absorb - but I digress).
But Stark... he's just human with no special abilities, well - besides being a genius, billionaire, playboy, philanthropist.
Yet, he uses all 6 Stones simultaneously wielding the Infinity Nano Gauntlet and doesn't instantly evaporate as we have seen with other beings.
Is this lazy writing or is there a plausible explanation besides "nanotechnology was specially designed to help Tony Stark but was disabled for Hulk."