I didn't necessarily learn these the "hard way" but here's a few lessons I think are important:
There are different types of love, but few if any at all are unconditional. The closest type to unconditional is a mother's love for her son/daughter. It matters who you are and what you do.
That said, some people will never love you, and some people probably always will.
Particularly in a relationship context, everyone is entitled to their deal breakers regardless of what they are. Nobody owes you a chance to be with them under any circumstances.
If in a relationship both parties are constantly wondering what the other one has done for them lately, something is very wrong. Both should be wondering what you've done for her/him recently.
You boost your own self-esteem from the little things first.
Hard work is integral to success, but it's not the only factor.
Thriving at anything requires some combination of talent (skills/ability), work (dedication), luck (stumbling upon opportunities/opportunities opening themselves up to you), and nerve (willingness to take a leap when the opportunity arises).
Life really is kind of like a movie that you're the star in, but you're the only one who's watching. They're the star in their own movies too.
Ultimately, you are the arbiter of your own happiness.
It's never wise to wager more than you can afford to lose.
Social skills are probably the most important asset you have in life.
If you have a good head on your shoulders, you will usually find a way in life at some point.