New players of poker often say that luck is the deciding factor of whether we win or lose. Even thought a bit of luck truly helps a lot, in reality the deciding factor is almost certainly the mistakes made during the game. Mistakes range from basic ones to those that even professionals make from time to time.
In the case of beginners, there certainly is no lack of mistakes made. Beginners are very often influenced by watching poker games in TV or other media. They don't realize that 80-90% of poker footage from these sources is edited; instead, they assume that it is important to play a large number of combinations. When calling or checking, they usually play based on their intuition, which is generally a bad idea for beginners. First and foremost, when beginning it is important to play primarily top combinations (pairs from AA to 77 and also AK and AQ), and to have a grasp of poker mathematics. That means knowing how many cards (so-called outs) we can still get to make our combinationa winning one. After losing a game we thought we had in the bag and losing a large amount of chips, it is generally a good idea to leave the table. Getting a breath of fresh air outside, or for instance getting something to eat or drink, will help us avoid reckless actions which could mean an end of our tournament run.
It is very important to avoid stubborn moves. For instance, do not stubbornly wait for a winning card while losing a large amount of chips. Beginners often end up waiting for a winning card, which in the end turns out not to be winning. Stubbornness can lead to a won game or two, but will almost certainly not lead to victory in the tournament. (Or maybe once in a lifetime it could, but the probability is really very low).
Beginners often have problems assessing the value of the cards they have in hand. For instance, they could start with a strong QQ pair before the flop, but the situation changes completely after a K, 2, A flop. The probability that they will get a third Q at this point is about 8%. And they don't even know whether their opponents have an AA or KK pair. If they have two cards of the same suit, then the probability to get two more cards of the same suit is about 11%, and even then they aren't guaranteed a win. It all boils down to a good analysis of the game, which in turn depends on our poker experience. This means adjusting to the situation in the game and avoiding stubborn plays – our actions should be based on what we have learned. Let us consider another phase of the game which is often problematic for beginners. Before the flop, most beginners only call, even though it is often better to raise and play aggressively. If they only raise when they have top hands, experienced players will quickly read their actions and then take all their chips.
In the end, everyone is just human and can make mistakes. But to make sure that the number of mistakes is as small as possible, one needs to work on his or her play. That means playing one's first games of poker in an environment which minimizes the beginner's losses. It also means studying all available literature, learning from one's mistakes and advancing one's play. And if you do happen to win against other beginners, don't think that you already know how to play poker. That, too, is a mistake often made by new players.