a fault or a lack of something that means that something or someone is not perfect--- defect
a bad quality or feature of something --demerit
a fault in someone's character or in a system,organization,design etc:-- weakness
weakness 弱点；缺点,demerit 过失；缺点 defect 瑕疵；毛病；缺陷
从各词的意思上可以看出一些差别.本题问性格中的什么东西阻碍了他的事业发展.defect最贴切,人的性格一般都不可能十全十美,存在着缺陷,瑕疵,缺少达到圆满或完善所必需的东西,而非弱点、缺点或过失.性格中的弱点有时恰恰是优点呢.
这个解释得很清楚.