It is just a behavioral quirk and I’m sure it varies with people. Some of them touch their temples, some squint and look faraway (into the horizon, lost in their thoughts), some tug on their earlobes, some bite their lower lip…..I’m a ‘ceiling stare-er’.I stare at the ceiling wide eyed when I’m lost in thought. My son scrunches up his mouth to one side when he thinks deep and when he’s playing chess, he places his left palm on his chin and rests that elbow on the table and then goes deep into his calculations….my wife is a ‘random object stare-er’ when she’s cooking up new techniques to show me how useless I am !......it varies and some of us have many such quirks, depending on the situation.