Achievers work to meet personal goals, regardless of their mood. Underachievers don't consider goals, and work only when they are in the mood. Underachievers have to be supervised, pushed, nagged, threatened or bribed to finish a project.
Underachievers avoid responsibility, blaming everyone else and making excuses for their failures.
Achievers put their heart into their work, thus connecting positive feelings with getting ordinary work done. Underachievers remain bored, disinterested and resentful which undercuts their motivation to get work done.