Over the years, poker became very popular and the boom of online poker has added fuel to the fire. Also the need for poker books increased, so many have been written so far, some good and some not so good. But they all teach you one thing more than they should: they teach you how to play tight and tighter than others. Although being tight is good sometimes and discipline and honest play is important, when all you do is play tight then it is obvious that you will immediately be spotted an all the others will be to fear and respect you and your hands, therefore when you do have a winning hand you will not be able to win too much because no one calls your bets.
When you are so tight and you enter a loose game, where players play mostly for fun, then you have a problem. They will spot you game and even if you play it by the book, you will not be able to win your pots. They may be playing for fun but still they want to play as much as they can for the money paid and that is why they will stay clear from your big hands. If they see you one time as a rock, then it is difficult to win hands with a big value.
When calling someone a rock in poker it means that player is conservative and tight to the extreme, he plays only the best hands and his reactions and actions are always accurate to the hand he is holding. On the other extreme of poker player stands the player referred to as the fish, a player that is mostly inexpensively and plays bad hands, losing most of times. The idea is not to stop hunting good hands or to play bad one, the idea is that you should take notice of your game style and if you see you are too tight to correct it. Not because you are missing some good hands that can hit, but because you are missing a lot of big pots. When seen as a rock at the poker table, you are risking the worst thing of all: you are risking to play in such a way that even the bad player knows how to play against you and do not loose. This is what makes a poker rock and it can be the most unpleasant thing, even more unpleasing then losing a big bet with a not so good hand.