That rule of threes is one of my pet peeves. it is just an excuse to load up on more gadgets. One exception seems to be for many of us is redundancy in tools and equipment to start a fire.

Tjin nailed it in his response....

Going solo really has nothing to do with it or with how much gear you pack. When solo, everything - all the decisions, all the actions - for good or ill - are your responsibility. The situation is both liberating and burdensome at the same time.