#2 Going PG
In July 2008, WWE announced that it was going PG. The weekly TV programming and monthly PPV events suffered a great deal from the decision.
Chair shots to the head were banned now, John Cena's finishing move F-U was now called the Attitude Adjustment, profanities were banned, and medial personnel would rush in immediately if a wrestler suffered a cut during a match.
The move led to a major rating decline, but the profits were up, as has been explained in detail here.
WWE's decision to go PG alienated a large chunk of longtime fans but brought in new viewers in kids who would buy WWE merchandise and attend weekly events with their parents.
Cena became the epitome of a good guy, turning into a role model for millions of kids across the world. Despite the poor ratings, the decision made WWE a huge amount of money in the long run.
Also read: 5 babyfaces who returned to WWE as heels
#1 Kicking off the Attitude Era
By the mid-90s, WCW had given a major overhaul to its weekly programming. The birth of the nWo kicked off a new era with clear-cut babyfaces and heels being replaced with anti-heroes like Hollywood Hogan and Sting. Vince McMahon decided to change with the times and delivered a promo, stating that a big change was coming to WWE TV.
This promo was followed by WWE targeting mature audiences and pushing realistic anti-hero characters like Stone Cold and D-Generation X. The move was one that possibly prevented Vince McMahon's WWE from going out of business. WWE slowly got its steam back and went on to defeat WCW in the Monday Night Wars, buying it off in March 2001.