His Achilles' heel is his absolute loyalty to his friends. One day he may get betrayed by his fair-weather friend.
 Achilles' heel fatal weakness是正統的美語說法.
他最大的弱點就是對朋友百分百的忠心, 有一天很有可能被假朋友出賣.< >
If you got severely injured and became a vegetabe would you want to keep living?