Assuming the best of other people is usually the best position to assume.
Here are some reasons for this:
1) There’s a double-distortion going on in our interactions: we think that we’re nicer and more reasonable – and our foibles more loveable – than they probably are (call it +1 vision), while people who aren’t us see everything we do as a bit more irritating than perhaps it really is.
Assuming the best of others removes (at best) half of the distortion in our interactions, which is a lot better than nothing.
2) If we have a culture of assuming the best – in our families, or friendship groups, or with our colleagues – we can be hopeful of eliminating most of the distortion, and can relax a bit. The assumption that others will assume the best is liberating and makes it easier to say what we’re really thinking and try out new ideas and things.
3) It often fixes things. In the absence of concrete evidence of malevolent intent (or persistent thoughtlessness), things work better when you assume the best. A bright reply to the snotty sounding email that you received can often redeem it – either by showing the sender a different way of being, or (just as likely) by revealing their true (non-snotty) intent, or by opening up a chance to talk about the crappy day/week/month they’re having…
4) It’s also easier on you – it’s a nicer set of lenses for viewing the world, and it makes the journey easier and more fun… Which makes it more likely that you’ll be predisposed to spot good things, assume the best, and be gracious with the worst. It’s the start of an upward spiral.
So there you go. All the best.