Your brain processes sound binaurally (from both ears). It takes information from both sides and puts it together to give you better comprehension. If you have a hearing loss in both ears, you will need two hearing aids to help you hear better and eliminate the risk of auditory deprivation in one ear. If you are only using one hearing aid, you are forcing your brain to re-focus all of the energy to one ear, causing the other ear to lack both auditory input and brain processing. Usually the only time you would wear one hearing aid is if you have a hearing loss in one ear only.