The thing with planning and estimation is that it's really the actual work in microcosm - you're building a model of what you want to do. The tradeoff is - how

The thing with planning and estimation is that it's really the actual work in microcosm - you're building a model of what you want to do. The tradeoff is - how much time do you want to spend on the model, instead of building it? You can get an absolute 100% accurate estimate if necessary - i.e. by doing the project and seeing how long it takes. For tasks that are reasonably repetitive or normalised, this can be straightforward, and you can reuse old models. the problem is larger software projects (like a unique building) usually involves either (1) high levels of complexity, such as legacy data or large levels of integration or (2) a lot of otherwise novel aspects, such as a new bit of R&D.