If it's _painful_ you are doing it wrong
https://www.lesswrong.com/posts/bx3gkHJehRCYZAF3r/pain-is-no...
https://www.lesswrong.com/posts/bx3gkHJehRCYZAF3r/pain-is-no...
It's actually fascinating how an ancient proverb could line up with modern science so perfectly.
But yes, if you never train close to failure you will not grow, not past beginner gains, unless you take steroids.
There's not a discernible distinction for me. Which is why I always hate hearing shit like "It should feel uncomfortable but not painful." Like, no, it's FUCKING PAINFUL! It HURTS!