The RNG is rigged, like a Vegas a lot machine. How exactly? It's quite simple...and ingenious. When you begin Destiny, you character has an equal chance to find any exotic weapon. Once you get lucky enough to find one (any exotic-it doesn't matter which), your chances to find that exact same exotic increase. This has the direct effect of making it harder and harder to find exotics you don't already have, therefore the longer you play, the less chance you have to find the exotic you're missing because the chances are so low becuase by then, you've found 12 SUROS, 15 Truth, 10 Ice Breaker, and so many Vex's they just go straight to postmaster. This is why your friend who has Gjallarhorn will find it so many times, sharding it right in front of you, while you in turn, shard that beautiful SUROS he wants so bad and can't find. Destiny's RNG makes sense if player trading or gambling was included, but they cut those features because 10 year olds.