They're probably referring to someone who starts getting high everyday, and quickly becomes "smoked out" - We all know someone like this. I used to get high a lot (when I was 21-23), and I stopped because I noticed myself becoming a shell of who I once was. When I wasn't high, nothing was fun anymore. It started off as saying things like "Bro this would be so much more fun if I was stoned", or "Dude, imagine getting high and then doing X' - This soon turned into "I'm so bored. This would be more interesting if I was high".
Soon, I wasn't happy until I picked up an eighth and rolled up a blunt or packed my bowl. When I would stop, I would feel so numb. I soon got depressed, but luckily found a counselor and worked through that dark time with exercise and meditation. People really downplay how damaging getting high all the time can be.
It's strange though, because this doesn't happen to everyone. Some people can get stoned all day everyday and live a very happy, productive life. I wish I was in this category, but nothing good lasts forever.