Small, infrequent bursts of stress are beneficial, but permanent stress is very harmful.
Simply put, stress kicks your body into overdrive. Staying in overdrive permanently is very bad for your health.
You can compare that to sport. Going to your limits every once in a while can be quite beneficial. Going to your limit 24/7 without any breaks in between will reduce your output below what you’d be able to do normally and in the end will kill you.
It’s the same with about every positive thing: too much of it is usually harmful. Some water is required to survive. Too much water and you drown.
And yes, attitude can mitigate some stress but there’s a certain level of where it becomes unhealthy, no matter what your attitude is. Again, coming back to the sports analogy: Attitude can help you push further, but working in a labour camp until exhaustion will kill you regardless.