When the dealer shows a 4 in blackjack, the optimal strategy is to be more aggressive since the dealer is in a weak position. If your hand totals 8 or less, you should hit, as it's too low to stand on. With a total of 9, you should double down, as the dealer is likely to bust. For totals of 10 or 11, doubling down is also recommended to maximize potential. If your hand totals 12-16, it's best to stand because the dealer's 4 increases the likelihood of a bust. On totals of 17 or higher, always stand. Additionally, pairs like 2s, 3s, 6s, 7s, 8s, or Aces should be split, as this gives you a better chance of capitalizing on the dealer's weakness. The strategy revolves around the fact that a dealer showing a 4 is at high risk of busting, so you want to take advantage of that with strong or split hands.