According to Merriam-Webster's online dictionary a principle is:
Principles are the most fundamental pieces of truth. Adhering to principles is a proven way to reach success -- if the principles are sound and lead to the desired outcome of course. One example of a sound principle is honesty. Another is collaboration/teamwork. For a more detailed description of principles and how to apply them in life and work I suggest the book Principles by Ray Dalio.
Principles are often disregarded when emotions run high. Irrational exuberance itself is an example of a widespread loss of investing principles in a market. One underrated principle is to avoid re-inventing the wheel. If there is a problem in need of solving there is a good probability someone else in the world is thinking/working on the same issues. It makes sense to work together and build on the work done by those before us. This is the essence of science and the free software movement. To do otherwise (to work from scratch when it is unnecessary) is a waste of resources. Wasting resources makes society poorer. Do not contribute to making society poorer.
What are some of the principles you seek to apply to your own personal or investing?