“My reasoned choice is as indifferent to the reasoned choice of my neighbour, as to his breath and body. However much we’ve been made for co-operation, the ruling reason in each of us is master of its own affairs. If this weren’t the case, the evil in someone else could become my harm, and God didn’t mean for someone else to control my misfortune.” Marcus Aurelius, Meditations.
To hold a different opinion to someone else does not mean that co-operation is ruled out. Expressing what you believe is right for you (“In my opinion…”) does not need to be caveated with a “No offence, but…” added in fear of conflict. Being clear about what is right and what is wrong for you is paramount. Stating this with confidence requires assertiveness – not aggression nor submission. As Gandhi once said, “A ‘no’ uttered from the deepest conviction is better than a ‘yes’ merely uttered to please, or, worse, to avoid conflict”.