Unreliable workers cause timeline problems. They can't build the roof first or do the wiring before the walls are put up. If some guy quits, gets fired, injured, it can throw off other dependant timelines. Maybe now that Bob got fired for showing up drunk and hurting someone, framing is going to take 2 more weeks, and now the drywaller contractors window got fucked up, they drop the job, and now you have to find another drywaller contractor on short notice. Maybe you can't until 6 months, so now your plasters are gone too, etc.
