To me, the only reason why Momota tanked today in the R16 to Heo Kwang Hee and it could've been any other opponent, for that matter, thereby ending his quest at the Tokyo Olympics, is simply lack of mental strength just when it mattered most in the biggest tournament of his career so far. And, yes, I'm afraid it would probably continue to haunt him going forward at any major events , regardless individual or team world championships.
Well, his past two world titles (and one All-England championship, if you like) are history; as they say, past performance is no guarantee of future results. The next Olympics, Paris 2024, is three years away, by then he will be 29 years of age, I shan't indulge in speculations, too early for that (think Covid-19, his being banned for the Rio'16 OG, the vehicle accident in Malaysia. Heaven forbid!).
Therefore, all those talks about his physical condition post-accident recovery, that is after-effects (which the man himself denied affected him - he would've been ready even if Tokyo 2020 wasn't postponed as he was reported to have said before), the technical aspects of his game (whatever we argued might be missing or have fallen short though most of us all agree , at his best, he is still the most formidable and fearsome opponent the last couple of years), his consistency or lack thereof, the dearth of international world-class tournaments to play during the global pandemic (for which every player is in the same boat, more or less), the what-ifs, the would-haves, could-haves, should-haves, etc, - all miss the point. Period.
In other words, he became his own worst enemy, proverbially speaking. By the way, homeground advantage is a double-edged sword, it varies individually. To make matters worse, his unfancied opponent of the day actually played above himself.
On another note, it made Lin Dan's all-conquering victory at the Beijing'08 Olympics all the more remarkable taking into account his previous Round 1 debacle at Athens'04 four years earlier at the young age of 20 in his debut Olympic performance and the rest is history, a testament to his exceptional mental strength, tremendous willpower, dogged determination, and the kind of self-confidence that was often described (mistakenly, in my view) as swagger.