Creating a piece of art versus designing a product. To an artist, a piece of art is something which he creates withint he boundaries which he sets for himself. This can originate from his life experience, his perspective of things, etc. But to the viewer, he does not have to look at it the same way the artist does. No matter if you appreciate it or dislike it, it is not a question of right or wrong. There is no standard of measurement for a piece of art. A design on the other hand has to adhere to a set of rules; a framework of steps to take and requirements to be met. This framework is called the design process. The idea is first conceptualized in abstract terms before actualizing it through its various forms. I think this is the part where we can inject our creative juices. Since our idea is abstract, there can be multiple representations of it. I think we just need to reflect back on our idea consistently throughout the process so as not to side track.
That being said, it does not mean that designers cannot be artist at the same time. Take for example, the Esplanade has been the subject of scrutiny since its design was made known to the public. Some say it looks like two halves of a durian, others say it looks like a pair of eyes of a housefly. The Marina bay Sands casino is said to resemble three joss sticks. Yet such works of art are feasible to build! Therefore a designer can also be an artist... you just need to know when to be either one.