the feeling of burn

Arnold S once said "You can't grown without the burn." How important
is the feeling of burn/fatique when lifting weight in your experience?
In my experience, it was easier to get the burn when working on smaller
body parts and that is when working on them ONLY WITH BODY WEIGHT with
no irons. They've responded well and quickly.

I have hard time generating the feel of burn with bigger body parts
such as pec and I am not satisfied with my pec development.

How important is this burn/fatigue in inducing muscular hypertrophy?

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