Ultimately means "at the very end of the process." Your strategy of robbing banks with a water gun worked a few times, but ultimately it was unsuccessful.
Use ultimately when you want to stress that there are many different elements of something, but in the end there's one clear conclusion. The city parks department might listen to everyone's ideas for what to do with that empty lot, but ultimately they'll do whatever they think will serve the city best. Ultimately comes from the Latin ultimāre, meaning, lying at the very end.
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