Why a secret keeper?

[WendyH]

No: HPFGUIDX 189896

Hi -

I've been reading the posts here for quite a while; although, I never
participate, I enjoy reading everyone's opinion.

Forgive me if this has already been discussed.  Ever since I read
about secret keepers I wondered why have them at all?  Why do you
have to tell your secret to someone?  Why couldn't Lily and James
kept the secret to themselves?  It seems safer.  What is it about
Wizards that requires them to have a secret keeper?

Wendy