With very few exceptions — Apple Music being chief among them — every design decision from Apple is deliberate and extremely well thought out. As we highlighted not too long ago, Apple’s laser-focused attention to detail in both software and hardware is obsessive.

But when it comes to the iPhone, Steve Jobs’ crowning creation and the most profitable product to ever come out of Cupertino, Apple takes things to another level. It’s why former Apple executive Scott Forstall once boasted of keeping a “jeweler’s loupe in his office to check every pixel on every icon.”

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With that said, one of the more interesting design of the original iPhone was Apple’s decision to use rounded squares for iOS icons, a design that still persists to this day. It was hardly an arbitrary choice: Steve Jobs had been a big fan of shapes with subtle rounded corners for more than 20 years before the iPhone even launched.

If we go back to the early 80s when Apple was working on the Lisa, Steve Jobs became obsessed with rounded rectangles. In an anecdote originally relayed by Andy Hertzfeld on Folklore, Jobs hounded Apple engineer Bill Atkinson to develop software that could ably create such shapes. At the time, Atkinson had developed software capable of drawing ovals and circles.

But something was bothering Steve Jobs. “Well, circles and ovals are good, but how about drawing rectangles with rounded corners? Can we do that now, too?” “No, there’s no way to do that. In fact it would be really hard to do, and I don’t think we really need it”. I think Bill was a little miffed that Steve wasn’t raving over the fast ovals and still wanted more. Steve suddenly got more intense. “Rectangles with rounded corners are everywhere! Just look around this room!”. And sure enough, there were lots of them, like the whiteboard and some of the desks and tables. Then he pointed out the window. “And look outside, there’s even more, practically everywhere you look!”. He even persuaded Bill to take a quick walk around the block with him, pointing out every rectangle with rounded corners that he could find.

With Jobs pestering him at every turn, Atkinson got to work and eventually figured out a way to get his software to render rounded rectangles. As development of the Lisa (and later the Macintosh) continued, Hertzfeld relays that rounded rectangles “worked their way into various parts of the user interface, and soon became indispensable.”

And so, when the iPhone was released more than 25 years later, it wasn’t at all surprising to see that the iOS icons all featured rounded edges. Furthermore, Apple’s penchant for rounded corners is also evident in various apps, such as the chat bubbles in iMessage.

In contrast, look at how much harsher a chat UI with more pointed corners looks.

Broadly speaking, design gurus and psychologists have both said that there’s something more soothing and welcoming about rounded corners relative to sharp corners.

DesignModo points out:

Sharp corners interrupt thought. To visualize a sharp-cornered shape, the brain processes point A to point B, pauses for a bit and then goes from point B to C, and so forth until it completes the circuit. In the case of a rectangle, it takes your brain 4 computations to recognize it. With rounded corners, the abrupt pause never happens, and your brain only does one single computation as your eyes smoothly scan its edges.

If the intersection of design and psychology is of interest to you, UXmovement has an interesting piece on rounded vs. sharp corners that’s worth taking a look at.