What are the biggest bottlenecks when developing large projects? [closed]

Question

Let's say that my company was to develop a replica of MS Word (just as an example). What would be the bottleneck to the development process, assuming that one has infinite cash available and an organization like Microsoft? In other words, what are the most usual hindrances from developing such software fast? Let's assume that all specifications are in place and the organization is working perfectly, so we just focus on the software development until the product is ready to be shipped. Some alternatives might be: - Writing the code - Writing tests - Manually testing the end product - Rewriting the code due to poor design in the first place - Designing the code - Code review done by experienced developers - Designing GUI - Redesigning GUI based on alpha/beta-user feedback - Processing feedback from users - Waiting for alpha/beta-user feedback

Please use references in your answer or state your experience on the subject.