2) Jrue Holiday
In the aftermath of the Damian Lillard trade to the Milwaukee Bucks, teams were lining up to acquire All-Star Jrue Holiday, who was sent to the Portland Trail Blazers. The Spurs should have been one of those teams, given their need for a starting point guard, and Holiday would have provided them with playmaking, shooting, and defense.
While he might not have been the point guard of the future since he is 33, he was coming off a career year, and the Spurs could have extended him if he played well in San Antonio. It would have given San Antonio a great stop-gap option until they found a long-term fit. Instead, there is a big question mark surrounding the position, and they are struggling after having not upgraded that role over the summer.
The Boston Celtics gave up a lot to acquire Holiday, but the Spurs had plenty of draft picks and expiring salary to get a deal done, making it questionable as to why they didn't when there wasn't a better option on the roster. That missed chance is coming back to bite them in a big way, and as the losses pile up, it's hard not to see the decision to trade for Holiday as a mistake.