There is no Secret, just stop farming, stop using that time from having to complete your daily bounties... Play as much Patrol, Vanguard , and Crucible as you can. Rank up your faction of choice and just buy your damn legendary items. Play the game to earn your Strange Coins and Mote Lights which can be used for buying exotic items. I don't think its just me, but I always max out on Glimmer (25K) and I use it all up on buying garbage from "Cryptarch" so I can rank up there as much as I can. Each rank up on Cryptarch will reward your from the post office...a lot of my legendary weapons and body armors came from that as well. Playing on the harder difficulty helps you a lot because it spawns more enemies. It can also reward you best for daily and weekly missions. Getting a legendary item isn't hard to do, fully upgrading them is the real challenge. And farming isn't going to upgrade them for you. the Exotic bounty will have you do what you should have been doing to begin with...
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I don't know why everyone keeps saying to stop farming and start buying your gear from vendors. A lot of people prefer to farm for gear through adventure than buy through a vendor. Now, if they complain about it 24/7, then they should probably follow that advice and just buy it if they want it that bad; but I'd honestly rather grind for gear than to buy it. It just makes it more fun for me.