Genetics help to some degree, but the most important thing is the mind and the spirit. These two are even more powerful than physical characteristics that are passed on.
I love to be sore and when I feel sore I train even harder.
Bodybuilding is not only a sport but first an ART.
To be tired it is only in your mind.
If you don't like don't do it. But don't forget that: NO PAIN NO GAIN.
Yes it is better to keep training even if your muscle is still sore.