We do this for multiple reasons but most notable is the need to preserve our sense of esteem.
Think of it this way.
Humans are self-preservation creatures (this is Life Lesson 101, by the way; know this and know peace).
And so, one of the major reasons found for this bias is the need to protect our self esteem. It’s all part of our instinct to be accepted in the tribe. And you’ll agree that constantly beating yourself down isn’t going to help that.
But also interesting comes the research that humans are apparently largely optimistic (shocking?). However this attribution is dependent on age and cultural background.

Probably the most fascinating find on functional MRI brain scans is the dorsal striatum (consisting of the caudate nucleus and putamen). Associated with the reward and motivation neural pathway, one theory is that positive attribution is rewarding to our sense of self. And this further reinforces the behaviour. Simply put, it makes us feel good.

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Another is the prefrontal cortex which is associated with mental planning and control. I found this surprising because it proved that maybe we really are just lazy. If this bias is our default, it’d require mental effort to override. Energy we’re often just not ready to expend.
But what does this do? I mean, sure, it feels like something we sometimes naturally do (and maybe rightly so). So what about the times when we’re wrong and not being objective? Besides, what harm can it really do?
Well…

What’s the deal?

Studies have shown that in certain cases of depression, there’s a problem with attribution. But in a different way, a reversed way.
Instead, there seems to be a misattribution of negative things to self. And then comes the danger of a single story.
It’s dicey.
On the one hand, blaming ourselves constantly can have adverse effects on our mental well-being. No one should put themselves down always.
On the other hand, not taking the blame results in a lack of accountability and a lost opportunity to learn and truly grow.
As with most things in life, balance is key. It’s why I appreciate people at the top who also acknowledge the role luck had to play. Being ready is one thing, but being at the right place at the right time is another.
But a major step is even being aware of this bias in the first place.

I’d like to reiterate that the point of being aware of these natural biases is not to make excuses. But perhaps by understanding ourselves (and, indeed, others) better, we can live more productive, compassionate and peace-with-all-men lives. Like Br (below).