What Are the Challenges of Sketching?

When people think that someone with an m f a is doing urban sketching, they assume a lot of advantages you have when it comes to purely drawing. So i'm curious to know what are the things that came easily to you when you started working out of a sketch book. What was the the special challenges that you faced when you first started open sketching without even knowing the term o been sketching? "I had to learn some things about drawing, architecture and pen and ink and straight lines and perspective," he says.