What if humans went through metamorphosis?
Metamorphosis is not a rare biological process. 65% of all known animal species on our planet go through partial or complete metamorphosis. It's interesting to note that the fossil records of the earliest insects show no evidence of its existence. It was a later development, about 300 million years ago. Why did it happen? Perhaps the environment went through radical changes. Maybe it was a genetic mistake. What's for sure is that after many millennia it's still part of the animal kingdom's life processes.
Humanoid beings that undergo metamorphosis is a subject that pops now and then in fantasy and sci-fi. Maybe their civilization would have no "children," and no "family," since species that develop using this process don't watch over their offspring.
How would metamorphosis affect the psyche of these beings? Would they become another "person" after the transformation? Would they have massive passage rituals to guide them through? Would they lose the memories of the stage before?
Could one of them decide not to go through the process and retain their juvenile form? That "choice" also exists for some species; it's called paedogenesis.