When I was younger I thought I could've prevented the death of someone close to me. It's only now I realise I could not have even if I'd been on my best behaviour or anything. Things that happen in our lives have agendas and sometimes the best way to learn a lesson is to go through a situation and reep the consequences.
Sometimes life can be thorny and there's no easy way around it, you've just got to get through, sometimes stumbling and being pricked. (Mental image - the garden of thorns Maleficent introduces for the Prince to break through in Disney's Sleeping Beauty.
It's always better to have positive expections than negative ones because negativity steals possibility from the moment.
Hope this helps!