Unless you are counting cards, the house has the advantage over the long term. You may have big swings of luck, but it is nearly impossible to win more hands over time than you lose. Taking that into account, it is important to determine how large your bankroll should be and what your maximum wager size should be if you want to keep from running out of money.
For a normal sitting, most infrequent players should expect to sit down with 20 times their average bet. So a player with a betting spread of between $5 and $10 using basic strategy can sit down with $200 and expect to probably not lose all of his or her money in that sitting—he or she might even triple that amount. The reason you want such a large bankroll in proportion to your wagers is so that you can avoid losing all of your money before it can go back up due to variance. Also having an appropriately sized bankroll helps ensure the ability to perform multiple splits, double downs, etc. (all situations that are good for the player). Forfeiting these opportunities as a result of not having enough money can significantly reduce your odds. In layman’s terms, an appropriate bankroll affords players elbowroom to take advantage of opportunities and withstand the inherent ups and downs of the game.