1. Agile Design

2. Problems with software designs
Rigidity
Fragility
Immobility
Viscosity
Needless Complexity
Needless Repetition
Opacity

3. Rigidity Rigid software is difficult change
One change requires mods in multiple modules
Changes are more difficult than estimated

4. Fragility The degree to which it is easy to break the program
Small changes generate unexpected side-effects

5. Immobility
The code is not modular enough for reuse

6. Viscosity Software Viscosity Environment Viscosity
When design-preserving methods of extending the software are less easily achieved than changes that are not in concert with the overall design (i.e., hacks are easier than following design) the design has “high viscosity.”
Environment Viscosity
The process of making changes (e.g., compiling, getting approval, configuration management) can also encourage a “quick-and-dirty” fix, rather than a fix better suited to the long-term maintainability of the system.

7. Needless Complexity Preparing for unknown extensions Bad Algorithms
Overly flexible
Bad Algorithms
Bad/Out-dated assumptions about system priorities

8. Needless Repetition Cut and paste is evil in software engineering.
How many places does the same processing occur?
That is the number of places that changes/fixes must be made
Do people understand what the cut and paste?
This is how software the literally no one understands enters the system.
The same code, with minor changes, makes the minor changes easy to miss.

9. Opacity How clear is the code
Code tends to get less clear as it is modified
Code tends to get less clear when you think about something else for a while
Code that is clear to you, might not be clear to others