“Impossible” personality is what we call “Shudra” in Vedic tradition.  In Vedic tradition, “Shudra” is not defined based on birth.  The “impossible” personality, the person who is stuck with the “impossible” personality, means doubt on yourself, doubt on others, doubt on your ability to relate with others, when you are stuck with the “impossible” attitude, you are “Shudra”.  

But you are stuck with self-doubt, but you don’t have any doubt towards your ability to relate with others, then you become “Kshatriya”. 

Your doubt on others, whether others can do or not, only that is there, but otherwise you don’t have doubt about yourself, then you become “Vaishya”.

If you have completed with all the doubts, neither you have self-doubt “whether I can do it or not”, nor you have doubt on others “whether he can do it or not”, or you don’t have doubt towards your ability to convey, inspire the other person, all doubts are complete, you become “Brahmana”.

Understand, it is just your personality which makes you Brahmana or Kshatriya, Vaishya or Shudra.  The community based on understanding and ability, not by birth, community based on understanding and ability, not by birth, that should be the lifestyle.