In Blackjack, just like in the real world that we all live in, there are facts. In the real world we have economic science. In Blackjack we have Basic Strategy. Basic Strategy is a statistically-proven list of plays, that if consistently followed, is guaranteed to give the player the absolute best odds to win against the dealer, in the long term.
For example, a player that has been dealt a 16 should always hit (request another card) , and risk busting (going over 21, and losing the hand), if the dealer has a 7 or higher. This is because we should always assume that if the dealer has a 7, he will end up with 17, thus beating the 16 (there are more 10s than any other card in a Blackjack deck). The C players many times are too afraid to request another card in this scenario, and would rather wait and see if the dealer himself will bust. More often than not, the coward player will lose that hand, which is why he is better off taking the risk of requesting another card.