Basement.org has an good article regarding Why Do We Love Rounded Corners, which is partly based on paper Information Object.
It has well says over the linkage of things, or looks we prefer, to the leverage physical experience of how we interact and use object. So rounded corners are preferable because human are attracted to things tha t appear to be organic in nature. And comparing to plain old rectangle boxes, rounded corners indicate more information (and more related) to the object it contained.
I am only wandering is it because we feel circle is prettier than rectangle? Our body naturally being rounded, rounded corners in physical world are less harmful.… (e.g. a rounded table compare to table with right angles).
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