Good at the beginning
...is another word for lucky. Someone needs to get lucky, and it might even be you, but luck is not a strategy.
Becoming good in the long run, that's the result of effort and tenacity and smart practice.
Not just the individual, the kid who doesn't learn to walk the first day, or the violinist who doesn't win a competition at the age of eight, but organizations and their projects as well.
The people who are good in the long run fail a lot, especially at the beginning. So, when you fail early, it might be worth realizing that this is part of the deal, the price you pay for being good in the long run.
Every rejection is a gift. A chance to learn and to do it better next time. An opportunity to figure out how to bounce, not break. Don't waste them.
Sometimes, getting lucky at the start means that you fail to learn resilience and tenacity, and you lack the tools to get better. The long run is a lot longer than the start is.