the only challenge that i can think of which really matters is adoption. and that is not something you can fix, it is something that is fixed on its own with time.
as time goes by more people find out about bitcoin and more of them start using it. some are merchants and some are users and they all make the ecosystem grow.
I think the common challenge for bitcoin users are the other user, we don't know what they can do. They can be one of those scumbags. They can be a thief that will stole your possession at any cost and at any time. Lastly, the most common challenge is the value of bitcoin itself, for its value varies everytime. It either increases or decreases.