In Blackjack, the dealer's upcard significantly influences your decisions. When the dealer shows a weak card (2-6), you're more likely to stand with hands of 12 or higher, as the dealer has a higher chance of busting. With a neutral card (7-10), the dealer likely has a strong hand, so you're more cautious about standing on 12-16 to avoid busting, while you may hit or double down with softer hands. If the dealer shows an Ace, it's a very strong card, so you should be extra cautious, especially with hands of 12-16, as the dealer is likely to make a strong hand. In general, the dealer's upcard helps you assess whether to be aggressive or conservative with your plays to maximize your chances of winning.