Conclusion
Working on code in small pieces is less risky than other means of creating software. Mitigating risk is key to ensuring project success and survival, because you simply don't know what will happen. Gradually evolving your code over time is the most surefire way of accomplishing your project goals without unnecessarily risking the project itself. Whether you're writing new code or improving existing code, doing so a little at a time is the best way to avoid mistakes.