Any given program will expand to fill all available memory.
Investment in reliability will increase until it exceeds the probable cause of errors, or until someone insists on getting some useful work done.
If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong.
Every solution breeds new problems.
Friends come and go but enemies accumulate.
The Ninety-Ninety Rule of Project Schedules - the first ninety percent of the task takes ninety percent of the time, and the last ten percent takes the other ninety percent.