I don't read it like that. Some people have a spidey sense for this sort of thing. I've only ever been laid off in my life twice. The first time I was completely blind-sided, because on a the Wednesday you have an all-hands meeting and see your name on the org chart the CEO puts up, and on Thursday they decide on a different direction. The second time was quite recent, but I already had one foot out the door, was actively interviewing, but the lay off came a little sooner than expected. Some people just pick up on the natural ebb and flow of a business and can sense when the winds are changing. I am as dumb as a box of rocks in most regards, but I have a good sense of when an organization is beginning to shift under my feet and no longer feels like a good place to stand.

To add a differentiator between laid off and fired, I've been fired twice in my life, once after I quit (toxic manager), and once when I refused to do something clearly illegal (another toxic manager).

how can you be fired after you quit? that's like somebody murdering you after you died. I'm all for asynchronous communication but some things are unavoidably sequential.

Give two weeks notice, and get shown the door that day?

In Germany that results in a mutual agreement to end the job contract. I would call that quitting without notice.

Certainly awareness of your performance, your relationship with your manager, what's happening with the company/your project etc. all may send signals that it's time to start looking elsewhere. But sometimes executive decisions happen without a lot of warning. And sometimes, to the point of a lot of the discussion here, something may be affecting the sector as a whole (or wider) so it may not be easy to find another position. A lot of people who post here seem to assume that getting a new job is something you send a few emails about and expect to get deluged with interview offers. That's not true of many people even today and certainly isn't true at all during downturns.

It also seems to conflate 'laid off' with 'fired', which makes it a little harder to understand. Is GP saying he would have been fired (for cause?) at these jobs? Or is this just using the term 'fired' in the colloquial sense of 'involuntarily terminated, for whatever reason'?

Layoffs are usually seen from a mile away. If you pay attention and don't want to go through a layoff it does not take luck or effort to leave before. I, for one, went through several layoffs that were completely predictable. I don't mind getting WARN money and some severance but some people feel that they are better looking for a job without competition from their former colleagues.

It can mitigate the chance of being laid off. Keeping your head down and working hard isn't enough anymore.

It never was. If everyone else is doing that then your value is a commodity. At some point soft skills and other differentiators come into play most of the time.