The two basic rules for successful speculative trading are "cut losses short" and "let profits run"; however, these two rules are mostly

Few people can achieve this.
When making a profit on paper, most people become risk-averse, preferring to cash out small profits and immediately secure minor gains rather than holding on, unwilling to take wise risks for larger profits. However, when facing losses on paper, most people turn into risk-seekers, unwilling to cut their losses in a timely manner.