Slack

is the title of an excellent book by Tom DeMarco (one of the authors of Peopleware). As usual I'm going to quote from a few pages:
The more efficient you get, the harder it is to change.
The survival tactic that Harry and others like him hit upon when their buffers begin to empty is to slow down.
The principal resource needed for invention is slack.
The purpose of the schedule was planning, not goal-setting.
You need to understand that management is utterly essential. It is.
Quality takes time.
You're efficient when you do something with minimum waste. And you're effective when you're doing the right thing.
When you're not safe, you feel afraid. And fear can inhibit change.
I see one pattern common to all winners. They acquire trust by giving trust.
We tend to resist learning things that really matter.
Most of us don't learn well from abstraction. We learn from example.
Training - practice by doing a new task much more slowly than an expert would do it.
Managing your risks requires that you go at some slower speed.