Leaving a company after 16 years ?

I am baffled by extremely experienced individuals suddenly taking a bad call in life like leaving a company they had worked with for 16 years to work for a dot.com which "didn't work out" in a few months after they started. Makes you wonder about their judgement and / or their resilience. Are they someone who can only succeed in a specific type of a work environment where there is suitable structure and corporate cushioning to couch / hide any falls ?  Or were they fired from their last job ? Oh well, that's why its so important to have choices and so so important to have the connections to do reference checks with the right people.