The first time you do something, you just do it manually.
The second time you do something similar, you wince at the repetition, but you do it anyway.
The third time you do something similar, you automate. Automation Is Our Friend.
Examples:
The process of renaming a class. When you're using file-based source code and a file-based version control (such as CVS), renaming a single class is an ordeal. Use something like Read Write Grep and some ad-hoc scripts to make renaming a class more enjoyable event. (Or use Eclipse Ide -- or IntelliJ IDEA)
Build dependencies in C++. You really shouldn't have to recalculate these by hand. See the suggestions on Recursive Make Considered Harmful.
Programmable Day Trading (and other business automation)
construct a GUI test-free, by running it over and over again, frequently by using the debugger
Don't forget Tab Completion, just because you use it without thinking.
...
The Power Of Now may be useful for justifying automation's costs to the Pointy Haired Boss. Perhaps I should read it?
This violates the Zero One Infinity Rule. You should automate on the second step because you KNOW you will repeat it.
Compare with: Three Strikes And You Refactor
See original on c2.com 