Meh you will fight because you have to. Not because you will win. Don't stress so much.
I have this constant feeling that if I hit someone it wouldn't actually do anything to them.
It's the same feeling when dreaming.
there's a part of my brain that makes me feel that the kicks & strikes wouldn't do enough damage to defend myself.
I am also a very nice guy, so I don't want to hurt anyone.
If you've practiced BJJ then you already have a good idea of what you can do. And if you have training in striking, then you probably have had enough feedback there too. I've met very few people in MA that were so weak that their strikes were totally useless.
Sounds like the concern is not with your physical ability, but with the bigger issue of your mindset, i.e., are you emotionally capable of hurting someone. Heavy sparring certainly wouldnt hurt, but it may not be the answer, since the mindset is still not the same as in a streetfight, where you might really have to hurt someone badly to defend yourself. I suggest you approach this question by asking yourself first whether you feel that you have the right to defend your own life against attack, no matter what happens to the other guy. Like the last poster said, when you fight, you fight because you have to.
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