Billionaire businessman Bill Ackman's new IPO, Pershing Square USA Ltd., (PSUS), closed at $40.90 on its first day of trading, down 18% and below its IPO price of $50.5. The company's shares traded up more than 4% on Thursday at $42.71, still below the IPO price. The IPO was structured with an incentive offering one share of Pershing square Inc. for every five PSUS shares purchased, but this did not prevent a weak open. Ackman attributed the IPO stumble to retail investors. His disclosed holdings show a highly concentrated portfolio, with 11 stocks spanning tech, consumer, and real estate.