Obscurity. Not enough people you, know what you do, or know how good you are at it. You can even be obscure to people who know you well, because of...
Uncertainty. You're good, maybe even great, but your lack of total certainty in your ability infects your performance. Conversations are performances. Every social media post is a performance. Sales is a performance sport.
Laziness. You're not persistent enough. You quit too soon. You don't follow up on opportunities. There's not enough energy behind your actions -- so even though they're the right actions, people don't quite believe you. Remember that humans are moved to action by emotion and justify actions with facts. Not the other way around.