Hypothetical:
Boston wants Davis from N.O., and has the #1 overall pick in the draft.
N.O. is willing to trade Davis (they're tired of looking at his brow), but can't afford the #1 overall pick.
Boston trades from #1 to #2, in return for the last pick of the second round.
Boston then trades #2 for Davis.
Now, in that hypothetical, Boston clearly loses the first trade, regardless of who the players turn out to be, because the #1 is a bigger step up from #2 than just the last pick in the draft. Boston just doesn't care, because it's the second trade that it's looking at, so it doesn't matter than it lost the first trade and, in fact, it can look at that second round pick as gravy.