#3 Losing his invincibility

When Brock Lesnar ended the Undertaker's undefeated streak at Wrestlemania 30, a lot of us were understandably angry. It wasn't just the fact that a part-timer had put an end to one of the most respected winning steaks in all of sport, but the storyline leading up to it did not seem nearly worthy enough either.
One positive that did come from the decision was that the company had a genuine monster in its main event scene again. After losses to John Cena and Triple H throughout the 2012-2013 period, fans weren't quite sure how to treat the Beast. After Mania 30, however, we knew exactly what we were dealing with.
Lesnar followed up his victory over the Deadman by destroying Cena at Summerslam 2014, winning the WWE World Heavyweight Championship in the process. From that moment on, every time somebody stepped into the ring with Lesnar, it was almost guaranteed they would meet a bloody end.
The air that surrounded Brock during this period gave a different feel to the WWE and broke the monotony that existed in its main event scene. We all truly bought into the idea that the wrestling company had a genuinely dangerous fighter in its midst.
That is until Bill Goldberg made his return to the WWE, defeating the Beast in a matter of seconds at Survivor Series 2016. The former WCW Champion would then eliminate Lesnar in very short order at the Royal Rumble before finally losing to him at Mania 33.
While the feud with Goldberg did throw up many memorable moments, it definitely served to break the illusion that Lesnar was unstoppable. Seeing the likes of Samoa Joe or Braun Strowman gain a temporary upper hand against him during 2017 never really felt that special seeing as we had already witnessed the Beast on the back foot.
There's no doubt 2017 was still a successful year for Lesnar, but because of his rivalry with Goldberg, it never felt like a dominant one.