The job of an NBA general manager is to maximize value. Whether it's wringing the most that you can out of a player, a contract, or a trade, the mantra stays the same: maximize value.
This is not always easy. In a league with 29 direct competitors and only one champion, it's difficult to always be on the "winning" end of every deal. Because everybody has the same salary cap, motivations, and information, sometimes there are no clear winners. Sometimes deals just need to be done because they need to be done. Have a player that doesn't want to play in your city, a glut of guys who play the same position, or a need for a big name to put butts in the seats? Maybe "losing" a trade is better for your organization in the long run.
This is about those deals. The preemptive ones that may hurt at first, but—much like quickly ripping off a Band-Aid or muting the word "Trump" on your Twitter timeline—will save you from more excruciating long-term pain. Don't be scared, NBA GM. These are for your own good.