Murphy's Law
Not a bias
Murphy's Law is the saying 'anything that can go wrong will go wrong'. It is a humorous adage more than a bias, and it reflects how failures stick in memory while the many times things go fine are overlooked.
This is a popular saying rather than a research finding, and the memory explanation is a plausible idea rather than a tested one.
In everyday life
A driver swears the traffic lights always turn red when they are running late, forgetting all the times they sailed through on green.
You are convinced the supermarket line you choose is always the slowest one, and every time it stalls you mutter 'of course'.
Why your mind does this
Our brains handle small, concrete quantities well but struggle with large numbers, fractions and odds. Rounding, grouping and labeling let us make fast decisions without doing the math. For most daily choices, a rough answer is good enough.
Its family, in 30 seconds: Simpler numbers
How to spot it
Ask whether you are counting the times things went smoothly, or only the times they went badly.
What you can do
Use the idea as a planning tool: list what could fail and prepare a backup for the most likely problems.
Same family: Simpler numbers
SourceWikipedia