Who in their right mind actually pleads guilty in court unless they’ve made a deal prior to the trial?

↓ Transcript
Panel 1:
Vinnie the Mouth: "How are you doing Leo? Are you ready for this?"
Leo the Boss: "I’m as ready as I’m gonna get. So let’s get this over with already."

Panel 2:
[Vinnie the Mouth and Leo the Boss walk into the courtroom for Leo's trial.]
Leo the Boss: [thinking] "Show time!"
Vinnie the Mouth: "Murphie."
Murphie: "Vincent."

Panel 3:
[Murphie (The Prosecution) and Vinnie the Mouth (The Defense) and Leo the Boss take their seats in the courtroom.]
Steel Toes (as judge): "Leo Veronisci, you are being charged with felony racketeering and possession of sugar with the intention of distribution, how do you plea?"
Leo the Boss: "Not guilty."
Leo the Boss: [thinking] "...Obviously."