Players who are relatively new to no-limit hold'em sometimes overvalue the importance of "tells" in poker.
By tells we're referring to those actions, either physical or verbal, players make at the table that might give away information about the strength of their hands. In any live poker game, especially at the lower limits, it isn't uncommon to see players revealing information via such tells without being aware they are doing so. Players also will deliberately act in certain ways or say certain things to try to deceive their opponents, and thus might give away information to others who are able to see through such performances.