Curling

There are many animals whose defensive action is curling up. Some are quite good at it, in fact they are made for it. Porcupines, pangolins, hedgehogs.
Sometimes I feel as if people are awfully good at it too. The problem with curling though is that when only your prickles are showing then no one can ever get to know you. I think some people don't find this a problem because they have two, three, five, etc people that they are always uncurled for, so they don't feel the need to uncurl for anyone else.
I've heard people mock those individuals who come out and tell you their whole life story for no apparent. Sometimes it probably is just personality, but sometimes I wonder if it's because they don't have anyone to uncurl for, and so they uncurl for anyone that walks by, hoping that the favor will be returned, but it rarely happens.
Why are we all so defensive all the time?
Uncurl, maybe it's not even for something you need, but for what another person needs.