Comment by TeMPOraL

Fair, I was under the impression that some strains of influenza viruses are in the mix too, but apparently they're distinct and not part of the cocktail (surprising, given how the other viruses found themselves bucketed like this - they evolved to lose potency over time; I'd expect influenza strains would be on the same trajectory).

Still, my main point holds - you usually can't tell by symptoms alone, whether it's a common cold or a flu. In case you get severe symptoms, by the time you can, you've already been infectious for some time. So either way, the right time to call in sick is when you first notice the early symptoms - stuffy/runny nose, cough, headache, elevated body temperature. But obviously nobody does that, because it would mean calling in sick at random a dozen or more times per year.

Post-lockdown COVID was the only time I know of in the last few decades, and a brief time indeed, when it was socially acceptable to react to potential symptoms at the right time.