There are many difficulties in estimating how long a software development project will take. You cannot compare estimate for small systems to those of large ones. The rate of development is not linear as the project size goes up. It just does not scale.
Another common fallacy in estimates is that developers spend the whole day coding. You will be lucky if they get to spend 50% of their time in development. Productivity also depends on the task complexity. Expect to get around a thousand lines of high level code a year per developer.
Here is another tragedy. Sometimes when a developer just tries to get their part done, it is to the detriment of the overall project. Want to hear more depressing news? The first system built is hardly ever a usable one. Next time I will continue with ideas about design and development.
Mysterious Double Instance Hampering Performance - I study the existing code base. Confer with a colleague. Then I determine the optimal plan to change the functionality to load only a slice of all the dat...