One of the 5 Fundamental Truths of Trading is:
Anything can happen. ("Trading in the Zone", by Mark Douglas)
This may seem rather obvious. However, many trading schools (that usually charge astronomical amounts of money to teach trading basics) often only teach picture perfect examples of their trading methods. Then, when traders are subject to real life trading conditions, they find that the examples they saw in school are rare in real life. Thus, they may either make bad trades or not trade at all, waiting for those picture perfect trading conditions that almost never occur. This is one of the reasons that I focus my trading methods and learning on dynamic trading indicators and methods rather than static ones.
Here is another core trading belief of mine:
"Trading should be FUN!" Bill Williams (author of two trading books in my library, including "Trading Chaos")