Why we use (!IsPostBack) in c#?

Question

What is the use of (!IsPostBack)

if (!IsPostBack)    
 {
 // Validate initially to force asterisks
 // to appear before the first roundtrip. 
        Validate();
 }

Answer 1

https://www.codeproject.com/Articles/1024172/Global-Service-Bus-Architecture-in-Csharp

https://msdn.microsoft.com/en-us/magazine/dd569756.aspx