Nagito’s obsession with hope becomes "forbidden" when it crosses the line into radicalism. He often acts as an antagonist, pushing his peers into lethal situations to see how their "hope" shines under pressure. This behavior isolates him, turning him into a "pariah" within the group. His talent is forbidden because it is uncontrollable; he cannot prevent the tragedy that must occur for his luck to manifest.
The specific event of Nagito Shinomiya "losing a forbidden flower top" is a recurring tag and topic within fan communities on platforms like
: Nagito realized he couldn't win. To use the flower was to forget why he wanted it in the first place. The Choice