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Physics has a well renown law and it states that: every action  has an equal and opposite reaction. An you can very easily demonstrate this by
hitting your head against a wall, the result is that it will hurt.

On a more subtle note, when dealing with people interaction the same rule applies. If you try to inflict violence upon someone, that someone will try to do the same to you. Any kind of violence applies may it be verbal or physical. 

So if any action of ours has a reaction how do I live life without the fear of negative reaction?

It’s quite simple actually. If you constantly keep in mind that your actions will cause a reaction, you can always limit and expand your actions so that even the reaction is positive.

Action-reaction bla bla, let’s have an example: “If you work really hard and you’re kind, amazing things will happen.” Conan O’Brien.

To that I’d only like add a Smile, so work hard, be kind and Smile, amazing things will happen!
How long has it been since you were kind, worked really hard and smiled?