Here’s an old, but still relevant, post by Steven Sinofsky on shipping products,
http://blog.learningbyshipping.com/2013/05/01/learning-by-slipping/
Some excerpts,
“In order to slip you need to know the ship date. When people talk about projects shipping “first quarter” that is about 90 different dates and so that leaves everyone (on the team and elsewhere) guessing what the ship date might be. A date is a date. All projects should have a date. While software itself is not launching to hit a Mars orbit, it is important that everyone agree on a single date. Whether that date is public or not is a different question.”
“Interestingly, the error rate in short-term, continuous projects can often (in my experience) be much higher. The view of continuously shipping can lead to a “project” lasting only a month or two. The brain doesn’t think much of missing by a week or two, but that can be a 25 – 50% error rate. On a 12 month project that can mean it would stretch to 15-18 months, which does sound like a disaster.”
“When a task cannot be partitioned because of sequential constraints, the application of more effort has no effect on schedule. The bearing of a child takes nine months, no matter how many women are assigned. The Mythical Man-Month – Frederic P. Brooks”
“Quality is the most difficult to manage and why the test leadership is such a critical part of the management structure of any project. Quality is not something you think about at the end of the project nor is it particularly malleable. While a great test manager knows quality is not binary at a global level, he/she knows that much like error bars in physics a little bit of sub-par quality across many parts of the project compounds and leads to a highly problematic, or buggy, product. Quality is not just bugs but also includes scale, performance, reliability, security, and more.”
“Quality is difficult to manage because it is often where people want to cut corners. A product might work for most cases but the boundary conditions or edge cases show much different results. As we all know, you only get one chance to make a first impression.”
On the same topic, if you know that you suck at planning and factor this in next time, it might actually prove a little useful ;-)