#3 Splitting the roster

Roughly a year after Vince McMahon purchased WCW in 2001, the WWE decided it had enough quality talent to justify two separate brands. This predicated the promotion's first-ever brand split: one unique roster for Raw, one for SmackDown. Unfortunately, the talent pool wasn't as deep as they thought and within a few years, the brand extension was abandoned.
It didn't help matters that WWE played fast and loose with the hard separation that was supposed to entice brand loyalty. Too often, SmackDown superstars randomly made their way to Raw and vice-versa for no rhyme or reason and with little to no explanation. So when WWE opted to re-merge the brands again in 2016, long-term expectations were not very high.
While there are certainly benefits to having two separate brands, WWE just doesn't seem to know how to implement it effectively. The brand split may be hot out the gate, but eventually, the company reverts back to its loose strategy and their failure to remain consistent has been a major mistake.