Having felt mortal as of the time, Thomas Wayne wrote a letter to his son, Bruce, leaving it on the desk in his lair, in the case of his own death. In the letter, he explained the reason for his lair, and gave him a bit of advice, telling Bruce that he couldn't have both happiness and the truth, and though he begged his son to choose happiness, there was an exception if Bruce felt a true calling.
- "Dear Bruce, these last weeks I begin to feel very mortal, which prompts this note to you. Perhaps I'm being paranoid. I hope so. In any case, if you're reading this, then I'm dead, and you figured out that the entry code is... BRUCE. I'm sorry I had to hide this part of my life from you, because this place only exists because of you. Becoming a father made me want to be a better man, and I started asking hard questions about the family business. So here we are. As I write this, you're 12 and a fine, good-hearted boy. So I'm sure you'll be a fine, good-hearted man. But that's all I know. I don't know what happened to me or your mother, or how life has turned out for you. I don't even know how old you are. So I'll resist giving you much fatherly advice. Only this: You can't have both happiness and the truth. You have to choose. I beg of you, my son, please choose happiness. Unless... Unless you feel a calling. A true calling."
- —Thomas Wayne's letter to Bruce