I think the point is that you don't know the limit until you reach it and when you do it may be too late. Seeing a spike in stress doesn't necessarily mean you'll burn out or that it will last forever so many try to weather it out with unfortunate consequences.

But I guess YMMV, every person is different. Some can take more punishment and get more time to decide if they want to keep it up. Some may burn out faster than they can realize.

That is fucked up. We are human beings, not some machine to be measured by how productive we are.

I think you are missing the point. You can be productive for yourselfas wellas for other people ...