. . . undaunted!
un⋅daunt⋅ed – adjective
1. undismayed; not discouraged; not forced to abandon purpose or effort: undaunted by failure.
The door was locked, but he had the key! And despite the fact that he couldn't have turned the door knob even if he had somehow been able to get the key in the right place, he kept trying. . . and trying. . . and trying.
While I'm glad he never succeeded, I can appreciate the perseverance.