Most people describe having an increased sensitivity to basic sensations like sound and light long before schizophrenia incapacitates them. This explains the reason why hallucinations are categorized under positive symptoms for schizophrenia as the hallucinations can be pleasant although for a short period of time. Once the sensation becomes overly intense, the resulting distraction will make it hard for one to perform certain routine functions.
Just think for a moment if the room surrounding you becomes several times brighter, with startling and shimmering colors that are so intense you have a problem looking straight at the lights. Each corner you turn, you are faced with the same intense sights of bright colors. Just think of how easy it will be for you to think normal and behave normal as it is expected of you in such a world surrounded by colors.
Closely related to the above illustration is the auditory hallucinations that are known to create the same ugly effects on someone. This explains the reason why most schizophrenia patients have a problem concentrating on a given subject or task. It is hard for someone to pay close attention to another when talking to them, sticking to a particular line of thought, or simply understanding what is happening around them if all they are hearing are loud voices banging in their ears.
It is a well known fact that people with this disorder often hear some internal voices only peculiar to them. These internal voices alone can be quite terrifying and disorienting. Just think for a moment how it would be like to live for a day with voices that originate from within your head.