Confusing lucky with good
This is why internet successes fade. This is why amateur salespeople so often fail to become professionals. This is why one-off sports analogy stories make no sense. Successful at the beginning blinds us to the opportunity to get really good instead of merely coasting.
The only thing more sad than the self-limiting arrogance of the confusion between lucky and good is the pathos of the converse: confusing ungood with unlucky.
Most people with a big idea, great talent and/or something to say don't get lucky at first. Or second. Or even third. It's so easy to conclude that if you're not lucky, you're not good. So persistence becomes an essential element of good, because without persistence, you never get a chance to get lucky.