I don't, why; Because it would mean that there's basically no real consequence for our actions. I believe in infinite possibilty or something close to that. But I believe everything plays itself out in one universe and not an infinite series of them. Depending on the relation between these parralels, truth would become subjective instead of objective.
Believing in parallel universes also raises more questions such as how does it interract with our daily lives, does it switch from universe to universe where changes can be small or significant if so then there's no truth anymore. Anything anyone says can be true depending on his or her experience of reality. It would be incredibly inefficient for life to have to deal with this.
Or if it is fixed and in the sense of it being fixed, since every possibility possible is being played out you don't have any choice and everything is pre-determined.
It would mean that freewill doesn't exist and that you're trapped in whatever is coming your way and can't influence your situation at all and any thought or feeling of being able to do so is but an illusion that you can. You would be utterly fooled and trapped. Education is futile as you would only learn more about your entrapment without finding a possible escape and since it was pre-determined you went this route it be only more torture.
Everything is forever out of control
-confusious
But that doesn't mean we can't influence our situation, you can't hide a sneeze but you can choose the direction.
You can't control an itch but you can decide to ignore it or to scratch it.
Freewill to me is the ability of action, not the ability to control but to be able to get up in the morning by choice whatever consideration for that choice is made the action begins with that, a choice. Freewil can be inhibited by a lack of self ''control'' such as anger issues, tempraments fog the ability of clear/rational thinking and directly influence your ability to excersise ''freewill''. Freewill is then inherently connected and excersised trough discipline.
You can learn to control your emotions by discipline, and thus have a choice to not get carried away with them. What some people would call a ''strong character''.