not want to admit his fears and he certainly doesn't want to admit them to his friends. In fact, when Gus admits that he is scared, Bigger seizes an opportunity to exert his power and authority over Gus by teasing him. The plan, however, backfires when Bigger realizes that if Jack and G.H. agree to the robbery then Gus will too and Bigger would then have to either own up to his own fears of robbing Blum or go through with the robbery. So, in order to avoid being put in that situation, he sabotages the entire plan by attacking Gus.

This idea is summed up in the following passage:

Bigger was afraid of robbing a white man and he knew that Gus was afraid, too. Blum's store was small and Blum was alone, but Bigger could not think of robbing him without being flanked by his three pals. But even with his pals he was afraid. He had argued all of his pals but one into consenting to the robbery, and toward the lone man who held out he felt a hot hate and fear; he had transferred his fear of the whites to Gus. He hated Gus because he knew that Gus was afraid, as even he was; and he feared Gus because he felt that Gus would consent and then he would be compelled to go through with the robbery.

Bigger's fear of Gus stems from the plan to rob Blum's deli. As we learn early in the scene, Bigger is "fascinated with the idea of the robbery, and a little afraid of it."

However, Bigger refuses to show any fear to his friends. In fact, in presenting himself as unfraid of robbing Blum, he establishes his power over his friends and gloats about the possibilities. The plan, however, backfires when Bigger realizes that if Jack and G.H. agree to the robbery then Gus will too and Bigger would then have to own up to his own fears of robbing Blum.

Bigger was afraid of robbing a white man and he knew that Gus was afraid, too. Blum's store was small and Blum was alone, but Bigger could not think of robbing him without being flanked by his three pals. But even with his pals he was afraid. He had argued all of his pals but one into consenting to the robbery, and toward the lone man who held out he felt a hot hate and fear; he had transferred his fear of the whites to Gus. He hated Gus because he knew that Gus was afraid, as even he was; and he feared Gus because he felt that Gus would consent and then he would be compelled to go through with the robbery.

From a psychological perspective, this is a complex question to answer but the answer sheds a great deal of light and insight into the character of Bigger Thomas!

In short, Bigger pulls the knife on his friend Gus as a way to both vent and conceal the many conflicting emotions he is feeling at that moment: anger, resentment, fear, and impotence. At its heart, it is an act of desperation to exert power and control over a situation where Bigger feels no power or control.

The scene is prompted by the plan to rob Blum's deli. Blum is a white business-owner and committing a crime against a white is something Bigger has never done before. On one hand, he is excited to exert a kind of revenge for the racial oppression that he had suffered for so long. On the other hand, he fears this act because he knows instinctively that committing a crime against white will only spur more racial intolerance and injustice against him.

However, Bigger cannot share these thoughts with his friends; he fears they will judge him as being weak and afraid--which he certainly is but doesn't want to admit. To mask this fear, Bigger pulls the knife and fights Gus in an attempt to prove his power and conceal the fear and desperation that he feels.

Almost all of Bigger Thomas's violent acts can be viewed through this same lens. There are no clear cut motivations or reasons for his behavior, but rather a complex mixing of emotions of fear, resentment, anger, and lack of control and power.