居安思危 (In prosperity think of adversity)

The "居安思危" is also known as "In prosperity think of adversity" - though you are in a peaceful surrounding, you should still think of the possibility of danger. We should prepare for danger in times of safety. I came across this proverb when I had lunch with my mentor. What is the message behind this proverb he tried to hint me? I am not conscious enough? I am still thinking ...