"Soon" and "early" are similar, but they measure time from different points.

"Soon" measures the time after something. That can be after now:

I'm leaving soon.

Or it can be after a point in the past, like the point when the employee noticed that there would be a problem:

Why didn't you tell me about this sooner?

"Early" measures the time before something, like before now or before the time when something is going to start:

Let's go. I want to get there early.