- over-promising or outright lying
- believing in something/someone that's too good to be true
Sagittarius is about faith, ideals and exploration. When Mercury is added to the mix, logic takes a backseat to hope and curiosity. People want to know more, believe more, say more. The gates of the mind are thrown wide open, and this is not a bad thing. After Mercury gets past the square to Neptune (this influence will be finished by December 13th) it'll be full steam ahead. But from December 10th to December 13th, proceed with caution. It will be too easy to put your trust in an illusion, or mislead someone. Mercury in Sagittarius will be the elusive X on the horizon, and Neptune will be the mist that distorts it. If you catch yourself saying "I hope/wish that ____" during this Neptune square, slow right down.
If you have planets between 0-1 degrees Sagittarius or Pisces, you'll be especially susceptible to this energy. Mercury will remain in Sagittarius until December 31st.