Fear of success is tough one to diagnose unless probed deep and prolonged, as it may have bleak symptoms, barely comprehendible, but are strongly reflected in results. I have known a person who has grown with paucities and he refuses to grow up and acknowledge success. For a long time I have been wondering why he lives with self inflicted defensive cover in his communication, behavior and actions, till I probed for a long time to conclude he has built a protective cover to 'guard' against loss of what he has achieved so far. Most of such people are scared to commit to demands of a new benchmark and consider it as a 'drain' on them.
This in some way has equivalence to a new height record that a pole vaulter attempts, stretching his physical and mental limits. He tends to belittle and attach insignificance to a past record while focusing on what if he succeeds, partly mixing it up with fear of failure too.
Competencies play a strong role in keeping pace with success, if they are not overpowered by old sticky beliefs that a person learns to live with, hardening them to limits where they begin to harm. Even at organizational level, leadership suffering fear of success can inflict significant damage to the growth.
It is important not to lose sight of such fear and combat it to keep successes going for long.