[The Swift Programming Language guide](https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AutomaticReferenceCounting.html) has the following example: 

    class Person {
        let name: String
        init(name: String) { self.name = name }
        var apartment: Apartment?
        deinit { println(&quot;\(name) is being deinitialized&quot;) }
    }
     
    class Apartment {
        let number: Int
        init(number: Int) { self.number = number }
        var tenant: Person?
        deinit { println(&quot;Apartment #\(number) is being deinitialized&quot;) }
    }

    var john: Person?
    var number73: Apartment?

    john = Person(name: &quot;John Appleseed&quot;)
    number73 = Apartment(number: 73)
    
    //From Apple&#39;s “The Swift Programming Language” guide (https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AutomaticReferenceCounting.html)

Then when assigning the apartment to the person, they use an exclamation point to &quot;unwrap the instance&quot;:

    john!.apartment = number73

What does it mean to &quot;unwrap the instance&quot;? Why is it necessary? How is it different from just doing the following:

    john.apartment = number73


I&#39;m very new to the Swift language.  Just trying to get the basics down.

&lt;br&gt;
***UPDATE:***&lt;br&gt;
The big piece of the puzzle that I was missing (not directly stated in the answers - at least not at the time of writing this) is that when you do the following:

    var john: Person?

that does NOT mean that &quot;`john` is of type `Person` and it might be nil&quot;, as I originally thought. I was simply misunderstanding that `Person` and `Person?` are completely separate types.  Once I grasped that, all of the other `?`, `!` madness, and the great answers below, made a lot more sense.

All Forced Unwrapping Solutions on Gang of Coders

Total of 1 Forced Unwrapping Solutions

What does an exclamation mark mean in the Swift language?