It's fall. The trees are losing their leaves. This is a good reminder that like all things in nature, human development is not linear.
The advances our children make in cognitive or social emotional development are easy to celebrate. It is difficult find the positive in the regression that is an inevitable part of the growth process.
Babies are born with "primitive reflexes". These innate and involuntary reflexes such as rooting for a nipple or grasping at a finger serve as survival instincts. Primitive reflexes are lost as specialized neurons gain functionality with progressive mylenation.
The reflexes that insure survival as an infant cease to be an advantage as a child gains autonomy. A great example is the Plantar Grasp Reflex. This reflex causes the Plantar tendon on the foot to contact when the bottom of an infants foot is stimulated but disappears around 12 months just as a child begins to walk, allowing the foot to remain flat for toddling.
Next time your child has a regression in some area of development, remember that like all things in nature some must be shed in order to make room for growth.