The triumph for completing duality solo says to just "complete all encounters solo". Which I did and it took me 2 WEEKS and like 100+ hours of grinding. Just to find out it has to be done all in one sitting or without going to orbit or whatever. The amount of time I just wasted because of "wording" on this triumph is disgusting.
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That's how all triumphs work. Bungie uses vague words all the time to have flexibility to change things