A Self-Fulfilling Prophecy in The Super Mario Bros. Movie
In the movie, Bowser spends the entirety of the story believing that Mario is here to steal Peach away from him, since Bowser wants to force Peach to marry him, but she's growing closer to Mario instead.
The reality is, Mario and Peach only just met each other for the first time, and, although they are developing a close bond (with subtle hints of developing feelings for each other), the main reason Mario went to Peach in the first place was to enlist her help in saving his brother Luigi from Bowser.
However, all of this goes to show that Bowser is really his own worst enemy. If he had any sense at all, he would have given Luigi back to Mario, stopped his own campaign of conquest, and accepted that Peach has no interest in him and moved on.
But instead, because he's entitled to have Peach no matter what, he immediately tries to kill Mario out of sheer paranoia and envy and keeps Luigi prisoner and threatens to kill him to spite Mario. It was because of this, Bowser ended up turning the once normal Mario Brothers into the Super Mario Brothers, therefore making them heroes adored by everyone, including Peach.
Not only that, but also by providing an adventure for Mario and Peach to bond over and by trying to kill Mario to get him away from Peach, he ended up causing Mario and Peach to grow even closer together than before to the point where they are starting to flirt with each other and even hold hands, therefore setting the groundwork for them to develop a romance in the future.
So ironically, Bowser ended up causing the very potential romance he thought he was stopping.
As a wise old turtle from a certain animated kung-fu film (ironically starring Jack Black himself) once said, "One often meets his destiny on the road he takes to avoid it."
