What is the meaning of [A chain is only as strong as its weakest link. Or, a chain is no stronger than its weakest link]

“A weak part or member will affect the success or effectiveness of the whole.”, Martin H. Manser (2007). The Facts on File Dictionary of Proverbs. Infobase Publishing. p. 38. ISBN 978-0-8160-6673-5. Retrieved on 31 July 2013.