The idea that humans, no matter their good intentions, can't help but bring pain to those they are intimate with.
The Hedgehog's Dilemma is the philosophy that to open up to other people will inevitably result in pain or hardship as a result of that action. The name comes from an analogy involving hedgehogs (or porcupines) to represent the human psyche. It describes a situation in which a group of hedgehogs want to huddle together to share heat during cold weather, but to do so would they would end up hurting one another with their sharp quills. Though they all share the intention of a close reciprocal relationship, this may not occur for reasons they cannot avoid. This philosophy is where Humans Are Bastards and Humans Are Good can overlap. Even with good intentions, we can still hurt one another. It is the unchangeable differences between people's thoughts, philosophies and experiences, which leave them unable to completely understand others, resulting in inadvertent pain. In a conflict, no matter how much two people might long to make-up, if their personal philosophies differ to enough of an extreme that there can be no compromise, there is nothing to be done. Opening one's self up to loving or valuing other people is another source of issues, because their loss or betrayal would harm you immensely. Likewise, loving the wrong person can potentially bring you into physical harm should your romantic interest have dangerous enemies who might use you against him. It's Not You, It's My Enemies (Loving someone has opened them up to danger) and Love Hurts (Falling in love leaves you susceptible to the worst emotional pains) are common instances of this in action. The Shrinking Violet or Ineffectual Loner are often as such because they operate under this philosophy and in order to escape being hurt or hurting others, they avoid making friends. This is a common theme in darker and more psychologically oriented works. One thing to know, however is that a hedgehog's quills are only sharp when "activated", meaning that in Real Life the hedgehogs would not stab each other under this circumstance. Compare Love Hurts, Humans Are Bastards, Humans Are Flawed
Examples: Anime & Manga