You wake up and look at your phone. You turn on the TV while you eat breakfast. You check your phone during your commute. At the office, you stare at a computer until lunch, when you look at your phone again. Check that phone on the commute home. Kiss your significant other. Turn on the TV while you eat dinner. After dinner, watch TV while you're on your tablet. Crawl into bed, turn out the lights and stare at your phone until everything goes blurry.
Congratulations, you've just essentially stared into the Eye of Sauron for 18 hours. Feel like your eyes hurt? You're not alone.