Being nice is not all that nice

Yes. I am saying this and my parents might just disown me for saying something like this. My parents are one such breed who would ask even their backstabbers, have you had your lunch? If not you may join us and serve them killing their own appetite. And so is my bro and now here i am saying this, "being nice is not all that nice."
Just imagine you trying to help someone in distress and they mug you or cheat you. This has happened to me quite a few times, where i have been betrayed by those whom i had extended my hands to help.
Although such cheating experiences are a few with me, the intellectual theft has been a lot. By intellectual theft, I mean the ones in the corporate world. When you see someone stuck in some process issues, or needs some idea and with common sense, you resolve the issue. However, the same idea is shared with a larger group and that person takes away the credit without even mentioning a word about you.

Isn't this a theft?
Isn't this cheating?
Isn't this backstabbing?
Experiencing this, i would never go forward to help someone personally or professionally now. Not that i am craving for attention or appreciation. But it feels bad so i decide not to be nice when there is need. But is this the solution? I am not sure.

How to resolve this?
How to handle this?
And how to not get affected by this?

So here is an open question for anybody to answer