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.
Friends come and go but enemies accumulate.
Don't force it... get a bigger hammer.
If your project doesn't work, look for the part that you didn't think was important.
Enough research will tend to support your conclusions.
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.