A nice sport quote by the legendary Babe Ruth, that we can easily interpret in the business world. You can interpret it as: You can not win business simply based on your previous clients or reputation, but you will need to work hard to acquire new business.
Yesterday’s home runs don’t win today’s games.– Babe Ruth
Explained simply: The past is the past, you can not expect to win a game today due to yesterday’s performance. Similarly in business, you can not just wait and do nothing and expect to get business, unless (to an extent) you are a big company with strong branding.