What aspect of song-writing gave you the most trouble when you were a beginner?

This is for some research that I'm doing. You're input is greatly appreciated. If you feel like you are a beginner at song-writing right at this moment, then you're reply is pure gold to me and I want to hear it.

So what part of writing a song was hardest for you at first? Was it coming up with good original riffs? Or maybe you had a bunch of awesome riffs and couldn't figure out how to string them together. Was it chord progressions? Was it writing lyrics? Was it writing drum parts? I want to know!

This is a question about composing so please refrain from talking about EQ, mixing, or mastering issues. Thank you. :)