1. The only video you have the intention of watching when you get on YouTube at any given time. Which then turns into three lost hours you'll never get back.
2. When you have a really great YouTube video to show someone and you make them watch it. Then they suggest one. Which reminds you of one your friend showed you. Three hours later, you're still on YouTube. All because of that first gateway video.
Dude, where have you been?
Sorry, bro. I was on YouTube for like three hours. I clicked on a link and it was a total gateway video. I couldn't stop.