Capital is a major part of trading but not the only one. It in fluences the profit that comes in the loss that may occur when the market is very poor. Huge capitals attract huge profits when the bull is present, but when the bear is around the corner you smell a great loss if greed sets in.
Capital measures your possible profit and losses.
Huge capital can be if huge risk as well but that was not the mean thing in trading because the real player is how you manage your fund and the strategies used. Because no matter how huge is your capital if mismanage and never have control of it, losses can be possible in end. So, if you put a huge amount into trading be sure that you already have a backup with knowledge and skill otherwise, you will no longer see your money back in your pocket anymore.