I wouldn't say "most", but I once had to fight to get an exemption in a startup's proprietary information agreement. We were asked to sign this after most of us

I wouldn't say "most", but I once had to fight to get an exemption in a startup's proprietary information agreement. We were asked to sign this after most of us had been there six months, and I had to threaten to walk off the job if they couldn't be flexible. The way it was explained to me was that they needed to be able to claim ownership of anything I did for the company or using the company's technology. Since that could include things I did outside of work for the company's benefit or my own, they needed to be able to claim ownership over 100% of my "works of authorship" in accordance with "provisions of the Pennsylvania Labor Code" which they refused to elaborate on. I finally got wording added to my agreement for open source software, provided I didn't use any proprietary startup magic to build it.