It’s as simple as this:
Never attribute to malice that which is adequately explained by stupidity.
When something bad happens to us, as egocentric humans we have a tendency to quickly judge that it was the result of malice - of some bad intent.
That person that cut you off in traffic? We can often automatically assume they are a selfish jerk. But if we apply Hanlon’s Razor, we might consider that maybe they are just quite an unskilled driver and possibly didn’t even see us.
That person who turned up late? Similarly we can often automatically assume that they don’t care about wasting our time, but if we apply Hanlon’s Razor we might consider that actually they might just be quite unskilled at managing their own time!
I know oftentimes I’ll be certain of the worst (leaving no room for benefit of the doubt) and then later I’ll get further information and find out that that my assumptions were completely wrong.
Hanlon’s Razor is warning us to be careful when assuming bad intent, because it’s much less likely that we tend to imagine!
I’ll leave the last word for Goethe, who wrote:
Misunderstandings and neglect create more confusion in this world than trickery and malice. At any rate, the last two are certainly much less frequent.