Fantasy basketball owners can lie to themselves all day but there's no denying the fact that being an NBA executive is one of the toughest jobs in sports. You are managing a few of professional sports' biggest egos in one of the world's most visible leagues with media types waiting to pick you apart. You get paid a couple of million and get to wear suits for a reason. Plus, human error does exist.
That said, it's an absolute must that you put a lot of thought into every move because championships, national visibility, attendance, and credibility (not becoming a meme factory like the Cleveland Browns) are at stake. League higher-ups presumably know that yet they still find ways to screw up what should be obvious no-nos—like the basic Slam Dunk Contest format for instance. But we're focusing on trades here.
To be fair, the folks couldn't have predicted how badly they missed out on stars like Kobe Bryant and Scottie Pippen. But at the same time, this is Kobe Bryant and Scottie Pippen they missed out on. Other examples are just straight up robberies. Come shake your heads at The Most Lopsided Trades in NBA History.