Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure, or nothing.

The Open Door (1957)

This quote is often simplified into:
Security is mostly a superstition [...] Life is either a daring adventure, or nothing.
Or paraphrased:
Life is either a daring adventure or nothing at all.