If your drag is set too tight, it can cause your fishing line to break under pressure. When you set your drag, you want to make sure it's tight enough to reel in your catch, but not so tight that it puts too much pressure on the line. A good rule of thumb is to set your drag at about one-third of the line's breaking strength. If you're still experiencing line breakage, try adjusting your drag to a looser setting and see if that helps.