Thats true. For system complex enough you will spend more time learning system than modifying it. Thats why all developers love to write new code and mostly hate to suport existing, working, legacy code.
> If you have a month to plan a project in detail, spend it on four one-week iterations developing while you improve your estimates. If you have a week to plan a project, hold five one-day iterations. Feedback cycles give you information and the experience to make accurate estimates.
- Kent Beck, Extreme Programming Explained: Embrace Change (The XP Series)
It took 1 month dissecting spaghetti to conclude the task was impossible without a hughe rewrite.
5 months later, the feature was a 2 line change, that could be tested and shipped in an hour.