HARRY: Hogwarts will be the making of you, Albus. I promise you, there is nothing to be frightened of there. (1.2.43)
Did Harry already forget about the seven years of danger he lived through at Hogwarts? Sure he might think it's a safe place now, but is he naïve to never expect it to change?
AUNT PETUNIA: If you were really reliving their death, all you'd hear would be a screech of breaks and a horrific thud. (2.1.17)
Aunt Petunia flat-out lies to Harry about how his parents died. Why does Harry remember these scenes with her? Is he wondering if he is a similar parent, lying to his own son?
DELPHI: If you're in Durmstrang robes—well, you can fade into the background, can't you? (2.4.38)
Delphi is very good at fading into the background herself. She tricks Albus and Scorpius by lying to them from the beginning and manipulating them both to try and resurrect Voldemort.
HARRY: I'm not keeping them apart. (2.13.13)
Harry lies to Draco when he tells them he's not keeping Albus and Scorpius apart. He explicitly told Albus to stay away from Scorpius. Why does he lie to Draco about this?
ALBUS: I don't have anything to prove to my dad. (2.14.45)
Albus is now trying to fix his past mistakes. Is Albus telling the truth here, or is he deceiving himself?
ALBUS: I'm pretty sure you told everyone that was on the bottom of a lake. (3.14.31)
Why does Scorpius lie about the Time-Turner? It's irresponsible of him to keep it, but his keeping it does eventually lead to closure for everyone involved in the plot of the play.
AMOS: I don't have a niece. (3.18.13)
Harry initially thinks that Amos is lying to Harry about his niece, and he threatens to throw him in Azkaban. Is Harry overreacting here? Does he owe Amos an apology?
HARRY: You would have hurt me less if you had told me this then. (4.4.24)
Harry feels deceived by Dumbledore, and he takes out his pain on Dumbledore's portrait. How would Harry's life have been different if Dumbledore had told it to him straight for his whole life instead of leading him around with a little trail of clues?
HARRY: And did you keep it?
DRACO reveals the Time-Turner. (4.4.54-4.4.55)
Draco deceives Harry by keeping a secret Time-Turner, but Harry forgives him because he's able to use it to get his kids back. As the Head of Magical Lawn Enforcement, Harry is easily influenced and erratic when it comes to dealing out punishment.
HARRY: For this plan to work she has to believe it's him, without hesitation. She'll use Parseltongue—and I knew there was a reason why I still have that ability. But more than that, I—know what it is to feel—like him. I know what it is to be him. It has to be me. (4.10.33)
The only person who can pass as Voldemort is Harry. He's Polyjuiced into other people and hidden under his invisibility cloak, but this is the ultimate deception for Harry Potter.