Why didn't Koenig succumb like the others?

This episode is one of the weaker in the series. It is based on the old theme of the paradise syndrome, where a perfect life is complete happiness, complete serenity and total bliss.
Moonbase Alpha encounters the planet Piri and when Eagles are sent to investigate, the pilots behave erratically and their computers return erroneous data. When additional Eagles are sent to investigate, the earlier pilots are found in a state of happiness that appears to be artificially induced. With the exception of Commander Koenig, this condition begins to appear in the remainder of the Alpha crew. For reasons that are never explained, he is the only member of the crew who maintains his reasoning capacity.
Eventually, Koenig is the only one left on Alpha, but he flies back to Piri and once again encounters the beautiful woman who calls herself the servant of the Guardian of Piri. He learns that the Guardian is a machine that was built by the original inhabitants of the planet. The machine was designed to provide the perfect world, but it worked so well that the inhabitants all died off.
Since Koenig is able to cure Dr. Russell of the affliction, the Guardian orders the Alpha crew to kill Koenig. He manages to escape long enough to destroy the servant of the Guardian, which was a machine. Once she is destroyed, the crew immediately recovers and is able to fly back to Alpha in time. At the end, their long range scans indicate that Piri now has life.
The reason why this episode is weak is that there is never any explanation as to why Koenig is not affected by the state of intoxication. He travels to the surface and yet when all others are rendered incompetent, he maintains all of his facilities. Even though some of the other aspects of the episode are interesting, I never could make the leap over this major logical flaw.