Brock's unstoppable aura would be gone if he lost, clean or not. His first "loss" was at WrestleMania, but he wasn't pinned in that. His second one wasn't really a loss, it was just a failure to reclaim the WWE Championship (BattleGround). If he loses at SummerSlam, clean or not, it would be the 3rd time he falls short. That wouldn't look good for his credibility. When you're booked to squash the face of the company and the entire roster, you need to keep the momentum going, not have him fall short 3 times in a row. And here's one thing to remember, booking 101 says that whoever gets the upper hand on the go home show loses the match on that Sunday's PPV. So me, I'm counting on a Lesnar win