Every project has hundreds of steps/tasks to do. All of them need to be completed to launch a product.
We take the approach to ignore all other steps and focus only on the critical task that if not possible, will kill the project. Could be technical, it could be market acceptance, it could be regulatory (we are in the medical device area). Specifically, it could need to be made at a certain price point. It could be the customer cannot find it difficult to assemble. It could be the customer needs to use it everyday, 3 times a day for up to 30 days (compliance is a bitch). It could be a strength threshold. All of it depends on the project and no 2 projects are the same.
All efforts are directed to that step. If that problem cannot be solved, the project is killed and we can use our resources on other problems. We did not waste our time doing a dfmea, having the correct draft angle or any of the hundreds of non-priority steps.
Anything linear will waste resources. I have yet to experience any software that was not linear. If there is something out there, I’d be happy to take a look.