How is a poem born?

Does it begin with a memory? A message? A line you’ve been saving in your back pocket? Is it always spontaneous or can it be preplanned, outlined like a story or an essay? I’m curious as to how everyone approaches the sometimes daunting task of writing a poem. There’s so much possibility, so much freedom in the realm of poetry that oftentimes I find myself at a loss on where to begin. What is the creative process to conception? Is muse/inspiration necessary for that conception?

—Haeun