While watching To Inform and Delight, Milton Glaser pointed out the importance of making things look like just happened, and not that they were designed. For example, Glaser did this when he placed stickers all over paper and liked how some of them pealed up and made it into a poster. Not only did it just “happen”, but it was a simple concept.
I think the key to making things look like it just happened, or that it was supposed to be that way, is to keeping it simple. He makes simple pieces that last decades. His most famous design is I “heart” New York. It is one of the simplest designs, but it defines a city and an idea that is extremely powerful. He might keep things simple, and make them look like the just happened, but it is not that easy. There is a reason why people want to learn from Glaser, he is simply the best.