Why does Bigger pull a knife on Gus?

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.