No one is immune from a slump. Rafael Nadal went through one in 2015, Novak Djokovic endured a rough stretch after winning the French Open in 2016 and let's not even discuss Roger Federer's 2013 season.
At 22, Alexander Zverev is going through his first significant slump after an upwards-only ranking trajectory throughout his young career. Despite being the holder of three career ATP Masters titles as well as the reigning ATP Finals champion, the world No. 3 has not gotten past the second round since February.