a chain is no stronger than its weakest link
If one part of something is weak, it jeopardizes the integrity, quality, or effectiveness of the whole. I need to make sure that everyone on our debate team is well-prepared, since a chain is no stronger than its weakest link. A chain is no stronger than its weakest link, and our security will not be effective if any of the checkpoints are not functioning.
chain is no stronger than its weakest link
Prov. A successful group or team relies on each member doing well. George is completely out of shape. I don't want him on our ball team; a chain is only as strong as its weakest link.