it can be a range of things, from temperature problems, to humidity issues, to not being turned enough, to not being stored correctly, to rough transit, to genetics- so many reasons.
Since this egg was from a supermarket, it's probable that it was stored badly, maybe even refrigerated, which...
hatching eggs? Or eating ones? That isnt quite the same as supermarket ones, supermarket eggs arent meant to be fertilised so its quite a special thing to achieve. It can be really disappointing if they dont survive through to hatch after beating the odds
I have done this before, this egg is fertilised and was developing but based on your more recent threads, it quit around day 3.
I'm really sorry.
Do you actually have ducks already or is this an experiment/first time trying with poultry?