TNG - "Cause and Effect"
God this episode pisses me off, for two reasons.
A) The number three. The reason Data plants this over 2000 times (?) is because it corresponds to the number of pips on Riker's collar? I doubt Data would pick such an obscure reference.
B) Morgan Bateson. Great guest star in the sunrise of his prime that the show does NOTHING with. I'm sure there are plenty of reasons for this, but goddammit why do it in the first place if there ain't going to be any follow up. I'm glad this got some attention in TrekLit.