By being aware of the fact that human nature is consistently flawed, Friar Lawrence’s fallibility can be explained.
It is irony that Friar Lawrence initially wanted to bring two families back through the marriage of Romeo and Juliet, but not even having the formal approval and attendance of their parents, and later on trying to hide the marriage. He tried to make Juliet a nun in which way he could hide the fact about the potion and secret marriage. Friar Lawrence appeared to be illogical and unreasonable when he went against his own advices for Romeo and Juliet and overlooked the damage/catastrophe of their secret, hasten marriage. His self-interest of doing his duty as a holy priest to keep peace made him devise impractical strategies, and rush. These examples explicitly show self-preservation, of Friar Lawrence and following demise of two lovers.