C# Design Patterns

Question

Hello Developers,

I developed many applications of Windows Phone and Windows Store without any serious thinking of Design Pattern at Student Level, but in Industry at first they said to learn the Design Patterns in C#, Why one should keep in mind about Design Pattern? How Design Patterns help us to build the Windows Phone and Windows Store application? Can you proove how Design Patterns are most important and why?

Waiting for interesting reply from your side.