I have noticed that 'generally speaking' some players from "specific countries" tend to play a bit more aggressive, especially before the flop. Thus, always check to see where they are from and calculate that information into how to play them. Even then, you still can get caught with them sitting with hole cards of AA, KK, etc. But, in poker, as some have stated, "nothing is always" as poker can be very fickle at times. For example, before the flop, how many times have you had hole cards of AA, KK, QQ, AKs, etc and then get beat by trip 2s, 3s or 4s OR a Set, Straight/Flush on the river?
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Another note to remember, 60% of the the common cards are represented by the Flop so most aggressive players (no, actually all players) really want to see the Flop. So it is generally best to not be too aggressive before seeing the Flop, especially considering how many players have yet to play (POSITION).
Good luck,
Wally