There was some data from Iceland that showed about 50% of cases being asymptomatic. That's more optimistic than we saw originally, but not as optimistic as the most optimistic scenarios proposed.
(which matches some of the estimates for Italy)
https://it.finance.yahoo.com/notizie/coronavirus-castiglione...
Sure, the virus will hit some people much harder than others. There's a component there yet to be discovered. But those exposed must have some sort of response, even if it's just a series of stronger than usual headaches. Stuff like that goes under reported because "oh that was just a random headache". Said person might drink a lot and deal with hangovers so headaches are expected. Whatever.
My point is that these studies are not very thorough in following up on the response quality or even a requery 2 weeks later when symptoms got much worse.
Lies,damn lies, and statistics from personal health studies.
My father was pretty good at giving differential diagnoses. He always said, "everyone lives, you just need to figure out what they're hiding and not focus on the why." I laughed when "everyone lies" became a meme on "House MD". The even more sardonic truth is that my father even lied after being diagnosed with a bad version of pancreatic cancer! (squamous cell carcinoma of pancreas) They asked him how much he drank and said, "A little bit, not too much." I stopped him and said, "Dad, you drink at least a bottle of wine every night." Oncologist replied, "OK heavy drinker". When asked about smoking he said, "No I haven't smoked since I left the Air Force 50 years ago." I corrected him and said, "Dad, you smoke at least a cigar a night while drinking. That's a lot of second-hand smoke." Oncologist replied, "OK, smoker." Everyone lies, and doctors make especially bad patients.
Next bit is personal, about me. One day I had a headache. Slightly off from a normal headache, hard to explain. Not wildly off like a migraine...just slightly. I rarely get headaches. I didn't think too much of it but left work to go home and rest. Two days later, I woke up with the same headache. No drinking the night before (honestly). Said, hrmm that's weird. I'm going in to get checked out. Long story short, I have intracranial hypertension and it's starting to manifest in new symptoms (exact cause unknown). It's good that they caught it now because it can lead to irreversible blindness if not caught. My point is, even big things can have minor symptoms -- even if they're "everyday" symptoms. (Pancreatic cancer symptoms are upset stomach)
I've personally observed two households where one member had some sort of very nasty flu thing with a dry cough, fever and breathing issues (likely covid but no test available) and other members were just unusually tired and with a tickily throat. The later could be classed as asymptomatic and would never have considered covid but they clearly had some symptoms.
I partially agree. If you're infectious, then the virus is multiplying inside your body. Eventually your immune system is going to react to that and you'll feel it.
But it's also quite possible that you can be infectious before you feel ill.