In the commercial and military flying business there is a term controlled flight into terrain. This means that the pilots flew the aircraft into the side of a mountain or the ground with intent. That is they were in control of the aircraft when it hit terra-ferma.
This happens many times in the project world as well. The project performance management system says you need to spend a specific about of money each month to keep on schedule. This is a absorption rate for the touch labor. In agile this would be the number of story points.
But the bigger - actually biggest - question is what is our capacity for work? In the federal project management domain, this is answered by the Basis of Estimate (BoE) for the Work Packages and Control Accounts. This is developed from a variety of estimating techniques. Once these numbers have been developed, they are risk adjusted for Management Reserve and the Deming variances that are needed for the cost, schedule, and technical performance.
This concept is not always discussed in software projects, even on agile projects. Phrases like, we can deliver this project for 120,350 hours with a ± 8% variance margin, so we'll need that ± 8% in our MR bucket to cover any overruns or schedule slips.
Projects without these buffers end up flying into the side of the mountain, killing even one on board and making a big smoking hole where the project was. Having been in the military aviation business in the 70's there was a box on the accident report form, titled BBR. This was checked when the condition of the remains were burned beyond recognition.
Don't let the BBR box get checked for your project. Keep the basis of estimates credible and executable. By executable it means Plan the Work and Work the Plan. For all projects, not matter the product development method, there MUST be a plan and this plan has to be a credible set of steps needed to land softly on the end and not fly into the side of the mountain, while still in control of the project.