A tree grown in a cave does not bear fruit. --Kahlil Gibran
A tree planted in a cave would soon be stopped short in its growth. There would be no room for it to grow tall or blossom. It would only grow so far and then would grow no bigger.
Fear can be like a cave. We sometimes become fearful for the same reason we might enter a cave, looking for protection. But fear protects us from the new ideas and behavior we need in order to grow. Fear can keep us huddling inside it, watching life's opportunities pass by. When fear threatens to enclose us, we can take a deep breath and begin to do what we are afraid of doing. The cave will fade away as we step out into the sun, fresh air, and storms that are a part of growing.