Sentence:  In my younger and more <WSD>vulnerable</WSD> years my father gave me some advice that I've been turning over in my mind ever since. ‘Whenever you feel like criticizing any one,' he told me, ‘just remember that all the people in this world haven't had the advantages that you've had.' 
Meaning of the word marked with <WSD> tags:  More or most likely to be exposed to the chance of being attacked or harmed, either physically or emotionally.