In the world of sport, perfection does not exist.
Even the greatest sides to ever grace a football pitch had their shortcomings, small weaknesses that could be exposed by opponents. From the mesmerising Brazil of the 1980s to the devastating Liverpool team that's currently running away with the Premier League, every squad has its Achilles heel.
Now, there are varying degrees of this. Some deficiencies are only minor and - for the most part - have a little impact on the side's performances, while others are lay bare for all to see.