Originally Posted by Tyhan

All one needs to know is that aliens do not require sight for mind control, and all of your soldiers mind controlled = you lose the mission.

If you know that much about XCOM you also know that morale does not require line of sight either. Since you only have to plan on fighting Ethereals two times, and can abort every other Ethereal mission, with two exceptions the only time you fight psionics is when you're fighting aliens with such low morale that a single HE rocket, taking out two or three (and Sectoids can almost never survive even at the outside edge of an HE rocket), will panic almost all the remaining aliens. And they can't mind control you until they've recovered and then taken your morale down first.

Try it. Load up a game of XCOM and see what happens on a Sectoid mission when you lead with an HE rocket, or a blaster bomb if you've gotten that far. Everything else just falls into place.