This is a mental disorder where people feel the need to check things repeatedly
What is a mental disorder that needs to be check regularly?
Oh I'm sorry I thought you already knew what we were talking about, it is Obsessive–compulsive disorder (OCD) 
Oh!  I have heard of OCD before.  Is it a condition that can be cured?
I doubt that it can be cured because the cause is unknown
What are some of the symptoms of OCD?
Obsessive–compulsive disorder
Obsessive–compulsive disorder (OCD) is a mental disorder in which a person feels the need to perform certain routines repeatedly (called "compulsions"), or has certain thoughts repeatedly (called "obsessions"). The person is unable to control either the thoughts or activities for more than a short period of time. Common compulsions include hand washing, counting of things, and checking to see if a door is locked. Some may have difficulty throwing things out. These activities occur to such
Arithmomania
Arithmomania is a mental disorder that may be seen as an expression of obsessive–compulsive disorder (OCD). Individuals suffering from this disorder have a strong need to count their actions or objects in their surroundings.
Sufferers may for instance feel compelled to count the steps while ascending or descending a flight of stairs or to count the number of letters in words. They often feel it is necessary to perform an action a certain number of times to prevent alleged calamities. Other examples include counting tiles on the floor or