Why was the attack on the steamboat disappointing to marlow?

The attack on the steamboat was disappointing to Marlow because it disrupted his mission and highlighted the chaotic and violent environment of colonial Africa. Instead of focusing on his goal of navigating the Congo River and understanding the complexities of Imperialism, he found himself facing senseless aggression. This incident also underscored the unpredictability and danger of the journey, which contrasted sharply with his earlier expectations of adventure and discovery. Ultimately, it deepened Marlow's sense of disillusionment with colonial endeavors.