The most common strategy deviations are deck composition dependent. Unfortunately most strategy deviations are not this straight forward. Doubling down achieves this, and becomes the obvious choice here. The most likely outcome is player wins, and when this is the most likely outcome a wise casino player wants to have as much money on the table as possible. And if the dealer also draws to total of 21 the result is a push. The 5 would give the player a total of 21, which is a no lose scenario for the player. If the player some-how knew that the next card was a 5, the most financially beneficial play that they can make is to double down. Imagine a situation where the player has an initial 2 cards that total 16, while the dealer has a 7 as an up card. However in certain situations it becomes necessary to deviate from this strategy to gain maximum profitability over the casino. These actions are determined by computer simulation, and decision points become firm at around 400 million hands. It tells the player when the appropriate time to stand, hit, double down, split and if applicable when to surrender (this where the player surrenders half of their initial bet to the casino). In Blackjack, Basic Strategy is the series of decisions that a player adheres to so that they can incur the minimal loss of funds over time.