Sometimes the hardest thing and the right thing are the same.
The Fray - All at Once

Anything worthwhile is hard. Because it is the difficulties that make it unique and it is the uniqueness that makes it valuable.

Difficult roads often lead to beautiful destinations.
- Unknown

When you have the choice, always start with the hardest part first. By achieving the hardest part first you gain a strategic and physiological advantage.

Strategically, you are de-risking the project by removing the biggest unknown on time, money and effort. The outcome of the project becomes more predictable.

Physiologically, you are providing a proof case. If we can smash the hardest part, the rest is going to be easy. Lets get after it. We have made it up the hill and the rest is downhill. Awesome.

Check out the Engineering Rule Book for the other rules.