For example, when my grandmother fell ill, my family spent a lot of time visiting her. My mother, in particular, spent many days and nights there, and her biggest complaint was the complete lack of communication between shifts.
Every few hours, someone new would come into the room, read my grandmother's charts, wake my grandmother up, and ultimately misinterpret several important details. Thankfully my mother was often there to correct them and fill them in on what previous nurses/doctors had already done, but the net result was that my grandmother barely got any rest (being constantly woken for no apparent reason) and, had my mother not been there, a nurse or doctor could easily have made a critical mistake when continuing her treatment.
Another example, still the same grandmother. Even though her original condition improved (after having been rushed to a different hospital), she ended up going home with an entirely new infection which resulted in several more weeks of sickness and eventual recovery. The infection (C. Diff) is one of the leading Hospital-acquired infections and is in many cases totally preventable. It's hard to believe how many people die each year due to infections they pick up in hospitals.