5. Drafting Jahlil Okafor
In 2015, Sam Hinkie made his only unforgivable move. After selecting Nerlens Noel and Joel Embiid in consecutive years, Hinkie drafted yet another center in Jahlil Okafor.
At the very least, Noel was a modern center and one that was seen as the best player in the class if it were not for an ACL injury and Embiid was a generational talent with injury concerns. Meanwhile, Okafor was a dinosaur that just happened to be declaring for the draft right before the NBA realized these types of players were useless.
Okafor was a highly-ranked prospect, but he was an undersized, lethargic center who could not shoot, pass, defend anyone, or do anything on offense besides post-up. Hinkie was pretty advanced in his team-building philosophy, but this was the type of player that could only succeed before the early 2000s.
Okafor was almost immediately linked to trade rumors.
This suggests that Hinkie had some inkling and was going to sell him for valuable assets before the rest of the league caught on to the scam that was Jahlil Okafor, but he was unable to see it through as the Sixers brought in Jerry Colangelo shortly after this.
This was also a very weak class, with the only other significant contributor selected in the next few picks being Kristaps Porzingis, another big man, who also refused to work out for the Sixers and has not had a stellar career either. Devin Booker was taken ten picks later, but he was not quite the obvious selection he seems like now.
Despite these excuses, this was a massive error in judgment that led to the Sixers having to attach a second-round pick (that ended up being Nicholas Claxton) to Okafor just to get rid of him. Given the type of prospect he was, it is realistic to think the Sixers should have considered trading down even then, which would have put them in the Devin Booker range.