Mr. henley said, "in the rat race we call life, only the strong will survive." he may have been referring to

He means that we all live the same life, we are the “rats” but we are racing to be the best or strongest. For example some people strive to be the most wealthy or most popular. Each of us will face obstacles to reach our goal or to keep living. Also it might mean that to keep living or to keep going straight in life we have to be strong and ready to face people who are better than us and obstacles that might seem impossible but aren’t.