Ria - if someone is constantly winning high stakes on black jack, which unless you are counting is purely a game of chance, then you become "watched". They then watch the people around you to see if signs are being used to indicate it's an organised "counting session".

If you're doing it on your own (even harder) then you'll be watched from table to table, since as it's more or less a game of chance, the odd's someone winning big on every game is so remote, you must be counting to do it.

(from Wikipedia) The principle behind counting cards in blackjack is that a deck of cards with a high proportion of high cards (ten-valued cards and aces) to low cards is good for the player, while the reverse (a deck with a high proportion of low cards to high cards) is good for the dealer. A deck rich in tens and aces improves the player's odds because blackjacks (which offer a higher payout than other winning hands) become more common, the dealer is more likely to bust a stiff hand, and double-downs are more successful.

Contrary to the popular myth, card counters do not need savant qualities in order to count cards, because they are not tracking and memorizing specific cards. Instead, card counters assign a heuristic point score to each card they see and then track only the total score. (This score is called the count.) This myth was portrayed in the movie Rain Man, where the savant character Raymond Babbit counts through six decks with ease and a casino employee comments that it is impossible to count six decks. In the movie 21, however, card counting is portrayed as a very intelligent task which can only be undertaken by high-IQ top level students.

Basic card counting assigns a positive, negative, or null value to each card. As each card is dealt, the running count is adjusted by each card's assigned value. There are multiple card-counting systems in use, but a plus-minus count — such as the Hi-Lo system proposed by Harvey Dubner in 1963 and later refined by Julian Braun and Stanford Wong — is one of the more basic and illustrative systems.

In the Hi-Lo system, the cards 2 through 6 are assigned a value of +1. Tens (and face cards) through aces are assigned a value of -1. Cards 7, 8, and 9 have a value of zero, or are called neutral (so they can be ignored).

The Hi-Lo system is an example of a balanced card-counting system, in it there are an equal number of +1 and -1 cards in the deck, so a count of all 52 cards would result in an end count of 0.