3. They’re often accompanied by rainbows. In the story of Noah’s Ark, God sends a rainbow as a sign to man that he will never again flood the world. Rainbows are thus seen as a symbol of peace, as is the unicorn. Over time, the two have often been depicted together.
2. They’re mythological, but not so outlandish that we can’t imagine them actually being real. Unicorns are just realistic enough to be possible. After all, they’re basically just a glorified horse.