In SharePoint 2013, You can't store more than 5000 list items in a List. It sounds interesting!! Isn't.?? However you can change the threshold limit in Central admin to hold more than 5000 list items.
The limit imposed by Microsoft on List Items is to prevent the perfomance degrade in farm environment. The internal logic is that all sharepoint List items are stored in the same table in Content database. Whenever list items are returned to users, a lock is applied on the table which holds all list items for web applciation.
So what happens when the list threshold is reached in a particular list ? End-users, instead of seeing the content they requested, will see a friendly error message stating that "The view cannot be displayed because it exceeds the list view threshold enforced by the Administrator"