I've tried many times to think what I would like to achieve during my life time. But I feel this assignment is not the exactly same one as the assignment to think about the goal of my life.
That is, since "I" would be turned into "he/she" in "my sentence", the point of "my sentence" is not what I want to do by myself but what I want to be seen by others. So the sentence must describe accomplishment or achievement of my life that any one can easily understand. For that my sentence is as followed.
"He accomplished what no other person in the world succeeded in during the 21st century."
To be described as above, I have to do my best all the time of my life.