An obstacle could mean what is in you that is your own "worst enemy"-for example, the King/Cups can be overly compassionate or indicate guilty feelings; this could cause an obstacle. Every person with a sob story or every relative who make you feel guilty for not doing your family duty could create an obstacle to your goals.
I'd be most particularly wary of family. That's where emotional blackmail may come in as an obstacle, especially from a father figure.
As for vice, Cups are all about excess--drugs, booze, overeating, laziness. These, as well, can be obstacles, whether they are your personal obstacles or someone else's that you must take care of (like a family member who is an alchoholic).