Always, ALWAYS, remember that. You define who you are. Others may have influence, but their opinion of you is never as important as your own opinion. Be your own biggest fan.
When a nice person does something unexpected to you, treat it as unexpected – as not-the-norm – and look at what happened. Because if you hit the limits of a person who is always nice, something is going on that is not good.
Change is the only constant. Remember that. Embrace it. And know that, without the pain of change, you cannot grow as a person.
Don’t forget to do something for the future. I’m not talking saving for retirement or for a rainy day. I mean making a change today that will benefit you in the future. A change in thinking. A change in behavior. A change in something that will make you better in the future.