somewhere along the line: o que isso significa e quando usá-lo?

You're in the middle of a presentation and you're doing fine. Suddenly, you're not sure when or why everything went blank on your mind and you start improvising and of course everything becomes messed up. After the presentation, when you're discussing the results of it all with your classmates, you tell them how confused you are for what just happened. You say: I prepared a lot for that presentation. I had everything on the tip of my tongue and then somewhere along the line everything went blank and I stuttered through the rest of the presentation.

When something unexpected happens somewhere along the line, it happens at someone point during a period or activity. Most the times, you don't know what that line is at exactly. For example, you're in a good relationship and for a very long time everything is fine between you two until suddenly somewhere along the line you start fighting at each other and it feels like there's no longer love. So you break up. That's it for today guys. See you!