While this may be true for some players, it's taking things too far. There are good reasons not to watch, as anything visual can have an influence on our subconscious, and that includes one's opponent's technique, habits etc. I watch players whose rhythm, play, technique etc. is inspiring, but will watch someone at another table if my opponent does stuff I prefer not to let sink in. Of course I won't tell my opponent, even if they asked why I was looking the other way, I would apologize for being rude - but it's rare that anyone notices (maybe twice in 25 years?). Except that I instruct/coach, and will encourage anyone to make sure they watch whom they want to emulate in one way or other - or watch exclusively what's going on on the table bed (watch the balls, reaction of the cushions etc., largely ignoring the player).
Greetings from Switzerland, David.
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„J'ai gâché vingt ans de mes plus belles années au billard. Si c'était à refaire, je recommencerais.“ – Roger Conti