Many a young person has injured himself permanently through a single clumsy and ill finished (with a bad ending) lie, (which was) the result of carelessness born of incomplete training.

许多年轻人都这样：用一个简单笨拙而又草草收尾的谎言，用那天生缺乏训练的疏忽所导致的结果来伤害自己。