It's also not apply universally, so many pax who don't understand the system are quite confused as to why some airlines check boarding passes and others don't, e.g.
DO
UK airlines, Air France, Emirates
DON'T
Air Malta, Lufthansa, Swiss
And as the airlines who do check don't have the gumption to tell the pax to keep their pass handy, many get quite hacked off at having to get it out again.
All in all, an example of the poor customer experience that airlines are masters of.
asy1, you need to grow up and develop some empathy.