To be honest, I don't know if I have ever truly "overcome" my challenges. I've learned how to deal with them. I've learned to live with them. Maybe that's what overcoming them means to some, but to me, overcoming means leaving them in the past. It means whatever it is, is no longer a challenge or struggle. To me, challenges are sort of like dealing with alcoholism. It's always there, right under the surface. They don't just go away, but you can keep them under control.
I guess the biggest challenge I've dealt with is my expectations of others. Occasionally, this still pokes it's head out and I get hurt, but it's so much better than it was. I've let go of my expectations of others. I still have my basic expectations, like people should be decent humans (that, alone is apparently even too high for a good portion of people), but I have let go of expectations I have had for family and friends.
By letting go of my expectations, I'm much happier. I know exactly who I can and should depend on, and that's me. If I get help from others, that's just a bonus for which I'm extremely thankful. It actually sounds a bit sad, but it's really quite liberating.
Like I said though, occasionally, I "fall off the wagon" and get disappointed because I think people should want to act a certain way. I can deal with getting let down by people every once in a while rather than all the time. There was a point in time where I was angry, all the time, because I had no one to depend on. Then, one day, I decided I was done being angry and the only way to fix it was to realize the only one I can depend on is myself. When I find myself thinking that someone "should" want to act a certain way, I stop, take a breathe, and realize that I can not control others' behaviors, but I can strive to be a better me and I can act the way I would like others to act.
I am in charge of my own actions. I am in charge of my own happiness.