That would be true if they didn't sometimes take your cabin bag away from you and put it in the hold.

(The last time I flew with United Airlines, they did that. Then they cancelled flights so I had to stay in Chicago overnight, and wouldn't give me back my cabin bag with clean clothes and things in it. Then they lost that bag and I didn't get it back for another three days. That was about a decade ago and I have never flown with United since then, nor will I ever again.)