This is really terrible advice that just discourages people.

You absolutely can get significant improvements without (much) pain. DOMS during the initial stages is going to be the most uncomfortable part. Once you're past it, you don't need to push yourself to a breaking point, just to the point of mild exhaustion.

This will provide you enough resistance to gain muscle mass and improve the bone density to healthy levels.

Yeah, "no pain no gain" is probably the worst advice I've ever received. It encourages sedentary people to go hard for a week and then quit, which is the exact opposite of what works: starting with consistent easy sessions and adding progressive overload.

Dynomight has a good blog post about this[0], but applied to running rather than resistance training.

[0] https://dynomight.net/2021/01/25/how-to-run-without-all-the-...