"Just don't let your emotions get the better of you. Number one thing to remember, you'll do okay as long as you don't forget that."

There's no way he's going to remember that, this mission is hopeless. But he can't stop Jack from talking to her. He can try, but it's only going to make Jack try and sneak off to talk to her and that's a lot more effort than it's worth. Tenenbaum already doesn't want to talk to him, Sinclair thinks he can't sink much lower than he already is in her eyes.

A few seconds later, the coffee's ready and Sinclair pours them both a cup, taking it back and sitting across from Jack at the table.