https://www.roleplayerguild.com/topics/173794-the-craft/char#post-4734866

I answer this question at the characters tab of the RP.  My format or your.  Just need to make sure the RP specific stuff is included.  The WHY question doesn't have to be overthought.  "Because the idea sounded cool" is a reason.  Maybe a shallow one, but still a reason.  Teenagers do things for far less thought out reasons.  For my character, curiosity and a need for friends would fit.