Nadal after his 2014 RG title missed the whole summer hardcourt season including the USO due to injury (a period that he sweeped the previous year), then missed WTF and had a surgery in the off season, was even doubtful to return for the 2015 AO, then had to try to find his form back, then in 2016 started having an amazing clay court season but again got injured, pulled out of the FO, Wimb, and then without hitting a ball for 2.5 months rushed for a comeback just to not miss the Olympics for a 2nd time in a row, and now is again trying to find his form back. This is no simple decline, this was also a lot of bad luck with injuries and setbacks. It's not about giving excuses, it's about being fair and logical. You guys compare him to Federer, but Federer has been lucky to never miss anything until this year. So of course it's easier to keep momentum and stay consistant.