Who does the individual blame -- hold accountable -- for their own screw ups? The individual holds himself or herself responsible/accountable because only they as the highest authority can chose to be rational and hold themselves accountable. Even the seeming opposite wherein a person is irrational and claims some higher authority -- perhaps a God -- is responsible/accountable for their screw ups is acting on their own highest authority to make that choice. The individual is the highest authority.
The individual is accountable for his or her own actions and that correctly identifies the individual as the highest authority in their own life. What's the alternative? ...The complete contradiction that there exists a higher authority that's responsible/accountable for an individual's actions. Still, to make that contradictory claim it can only be asserted by the highest authority--the individual.
If the individual is not the highest authority the individual would not be able to choose either: 1, rationally account for their own screw up; or 2, irrationally hold another person or thing accountable for their screw up.
That is true, even when, as most people do, they abdicate both their authority and resposibility, surrendering their authority to any agency (government, religion) who promises them easy answers and thir responsibility to anyone who promises them security and guaranteed success.
Hank