You see a painting and immediately recognize that there must be a painter because we know paintings do not occur naturally. I mean, you can't go out to the woods and find an "art tree". Same with anything else that we know is designed i.e. watches, buildings, cars, etc.<quoted text>
When you see a painting, fo you question whether or not the painter exists? No. The painting itself is proof enough that a painter exists. Same goes for God and the universe.
We know that man-made objects are designed a posteriori. We have heard of designers. We know of companies that make such things. They are made out of plastic which doesn't occur in nature or finely polished purified silver which doesn't appear in nature. We know such things are designed because of our knowledge of the world we can logically conclude that they are designed
Seeing design in nature involves confusing the direction of causality. Humans are the product of a long evolutionary process that has adapted us to the environments where we live. That our surroundings seem well suited to us (to the extent that they are) is not surprising, but is not evidence that it was designed for our benefit; rather it is a testament to the power of evolution to produce well-adapted organisms.
Continuing in the evolutionary vein, one of the beneficial adaptations of humans is the ability to infer intent. This allows us to anticipate behavior on the part of other organisms that might be detrimental (or beneficial) to our survival. However, this ability can be overgeneralized; we can see intent and purpose where there is none. Seeing design in nature is an example, since the religious view is usually that the universe was designed for our benefit. Thus, inference of design is really a kind of fallacious inference of intent.