It's that level where you don't just do it, it becomes a lifestyle.
You quit just before you reach it.
"Dude, the way I see it, I'm on like, level three of smoking marijuana."
"Dude, just quit before you reach level 4: marijuana is your life."
Californian Prison code.
Level 4: Cells, fenced or walled perimeters, electronic security, armed officers inside and out.
Maximum securit for violent offenders, murderers etc.
"do a 187(murder)on someones ass, you gonna get a level 4, don't drop the soap!!"