Brush Trading

Ok, so you know when you're trying to 1v1 someone in the top lane and they walk in the brush, or every time you to hit them with an ability, they walk into the brush? Is this a common mechanic in League that everyone knows about but me, or is it just something the some players do? Because it seems like every time I follow them into the brush to continue the trade, it usually results in disaster. What are your thoughts? I didn't see anyone talking about this when I looked it up., and it happens so many time when I'm trying to fight someone that it's becoming ridiculous.