In Blackjack, the dealer's upcard significantly influences your strategy, as it provides clues about the strength of their hand. When the dealer shows a weak card (2-6), they have a higher likelihood of busting, so you can play more aggressively by standing on lower totals or doubling down when you have a strong hand. If the dealer's upcard is a 7, 8, 9, or 10, they have a more stable hand, so you need to play cautiously, hitting on totals like 12-16 and standing on 17 or higher. Against a dealer's Ace, the situation is more uncertain, as they could have a blackjack or a strong hand. In this case, it’s often better to play conservatively, standing on 17 or higher, and hitting on lower totals if needed. By adjusting your decisions based on the dealer's upcard, you can improve your chances of success.