If you flip a coin 100 times, your expectation is to receive 50 heads and 50 tails. But the reality may well be different; the measurement of that reality is called "standard deviation".
Standard deviation is a mathematical term used to predict the outcome of a situation. In our coin-flipping exercise, we expect 50 heads and 50 tails to occur, but two-thirds of the time the actual result will be somewhere between 45 and 55 either way. That is, a result of 55 heads and 45 tails or something in between is not unusual; it will happen 68.3% of the time. That measurement is for 1 standard deviation from the expectation and if we were to run hundreds of 'trials' of 100 flips, we could plot our results on a bell curve and the vast majority of results would fall between 55 and 45 either way. What would be unusual would be to have a lot of trials where the result was actually 50-50! Got that concept in your mind? Good. You'll need to understand this in order to survive the mental turmoil caused by the losses which are inevitable in this game.
Nothing has caused counters to give up Blackjack more than a lack of understanding about normal, everyday standard deviation. Counters who have trained hard unrealistically expect to win each time they play, so when they have several losing sessions, they forget what they've learned. Next thing you know, they're over betting their bankroll and fail to play their hands properly and when they wake from the daze, their money is gone.
PATIENCE AND SKILL WIN -- HUNCHES AND WISHING WILL NOT WIN. PRAYER DOES NOT WORK AT BLACKJACK.
So, what can you expect -- what's the worst which can happen? Well, you can lose all your money, but if you establish a bankroll of at least 50 'top' bets, play proper basic strategy at all times and don't over bet, you stand a good chance of making some $$$ at Blackjack -- if the game at your local casino is a game which can be beaten. Did I ever say this was easy?
The table below illustrates the possible results from varying hours of play at a fairly typical game. Shown with the expectation are the possible dollar results as measured by 1 standard deviation (68.3% of the time) and 2 standard deviations which covers what will happen 95% of the time. Three standard deviations cover what will happen 99.7% of the time.