What concept might undermine a strategy of self-defense?

The concept of "proportionality" can undermine a strategy of self-defense, as it requires that any response to an attack must be proportional to the threat faced. If a self-defense action is deemed excessive or retaliatory rather than protective, it may be viewed as unjustified aggression, potentially leading to legal or moral repercussions. This principle emphasizes the need for a measured response, which can complicate the justification of certain defensive actions.