The point is that at a company you are a line item in the budget and you will be forced out the moment it’s not financially beneficial to keep you around.
That generalization definitely doesn't hold for everyone. I've made so many great and lasting friendships from work over the years - even picked up some new hobbies and gone on trips together. If I'd come in with the attitude that it's a bad idea to make friends or socialize with coworkers, I would have missed out on a whole lot of life-enriching experiences.
This sentiment confuses me. Maybe it depends on the kind of company you work at, or maybe it's a cultural thing (I'm in the UK), but I've met many of my best friends through work, as have most people I know. It seems like one of the main ways to make new friends as an adult, and to be honest I've never experienced any downsides to it.
You should build your life outside of any company:
- mixing friendship with work rarely ends well, you might end up competing with your best friend for the same promotion, he might not even be your best friend, just making you think that he is
- dating in the workplace is a minefield, you can easily get into trouble
Don't be attached to a company, you can find another role in seconds.
You don't need to keep up with everything in the company, you just need to be good at what you are doing.
You don't need to be promoted at the company, you just need to improve your skills, it might be easier to leave and join another company, or even rejoin the same one in a more senior role than to go through the promotion process.