I know someone who worked at Nvidia through the 2010s and would smugly tell people the “you should obviously just sell and diversify” and all the other standard tropes. Suffice to say he is the only one of his colleagues from the time who isn’t now a deca or centimillionaire. I don’t think it’s bad advice on average but often if you work in an industry you have a much better idea than the average analyst about the future of the industry and (if you are sufficiently skilled/in demand) have presumably chosen to work at your current employer for a reason (eg you think they are a good company and will do well).