Clients often have difficulty understanding that a patent does not give them the right to practice the patented invention. A patent is a negative right in that it gives the patentee the right to stop others from making, using, selling… the patented invention.
In practicing your own patented invention you may be infringing the patent of another. As example serves to illustrate:
Assume that the basic automobile was still protected by a patent. If you were the inventor of an automobile with traction control then you would be able to patent your invention. However, in practicing your invention you must first make an automobile and then add the traction control feature. In making the automobile you will be infringing the automobile patent.