I think it's possible to overcome a nicotine addiction
Do you know anyone who has done so?
I know it has been proven, but I don't know any people who have successfully stopped.
You're right that it is possible to stop nicotine addiction. Smoking is pretty harmful for health so it's better to quit it.
I've been trying all day, I just can't quit, it's not easy.
That's great that you are taking the first steps toward quitting, but I have to remind you that it is a long process, and it won't happen overnight.  You shouldn't try to quit on your own, though, there are programs and medicines that will help you to overcome the cravings for nicotine.