You know exactly what you need to do. You even know how to do most of it. What you don't know, you find out. By thinking, reading, googling, thinking. Thoughts fly fast. Fingers fly fast. The code grows, takes form, shape. Code, compile, run, code, compile, run. Few compiler errors, few running errors - it all just works. Nice code, "feels right". Time flies. Before you knew it, a week's work is completed in a few hours.