Introduction

There is a proverb: “After victory, tighten your helmet strap.” When people get an early sense that something is working, they tend to want to push forward. But that very feeling of momentum can distort judgment and become the trigger for overlooking the next pitfall. The sense of “it’s going well” is an important signal that can indicate success, yet at the same time it can become a trap.

Why the Feeling of Momentum Is Dangerous

When something seems to be going well, the brain shortcuts to “this approach is correct” (overconfidence bias) and selectively filters for information that fits its expectations (confirmation bias). As a result, people skip re-examining assumptions and fail to recheck risks, scaling up based on a skewed view—small oversights can cascade into catastrophic defeat.

Concrete Example: Takeda Katsuyori and the Battle of Nagashino

In Japan’s Sengoku period, the Takeda clan was known across generations for its strength in cavalry and close-quarters combat. Especially under Takeda Shingen, they overwhelmed neighboring powers. After Shingen’s death, his heir Katsuyori inherited the clan’s domain and forces, but initially lacked experience and did not command the same level of support as his father. Nevertheless, Katsuyori aggressively launched diplomacy and warfare against surrounding domains. In 1574, he captured the virtually impregnable high fortress of Takatō Castle (note: the original text says “Kōtenjin Castle,” likely referring to a similarly difficult stronghold—if meant as 高天神城, it’s Kōtenjin Castle), which even his father had failed to take, and gained a strong sense of validation rooted in family legacy and that recent success.

That feeling fostered overconfidence—“Nothing can stop Takeda; the next battle will also break through.” In 1575, at the Battle of Nagashino, he faced the allied forces of Oda Nobunaga and Tokugawa Ieyasu. The allies had organized large numbers of arquebusiers (firearms) in disciplined formations and constructed palisades to blunt cavalry charges. Katsuyori, relying on traditional cavalry assault tactics, attacked head-on without sufficiently reassessing the changed enemy dispositions and firepower. The concentrated gunfire decimated the cavalry, resulting in a crushing defeat. This defeat marked the beginning of the rapid decline of the Takeda clan, which ultimately fell at the Battle of Tenmokuzan in 1582.

This is a textbook case of how past success and intuitive “momentum” created blind spots that caused failure to perceive real changes in the environment.

Three-Step Prevention

The euphoria of success can cloud judgment and produce consequential oversights. Being mindful of the following three points makes it much easier to avoid that trap:

• Pause
  
  When you feel momentum, take a momentary break. With the heat cooled, re-examine the current situation and underlying assumptions—distortions become more visible.




• Premortem
  
  Deliberately imagine and write down: “If this fails, what would have caused it?” This surfaces blind spots and tests whether previous assumptions still hold.




• Reality Check
  
  Briefly explain the situation to a friend or colleague and ask skeptically, “Where do you think I might be wrong?” An external perspective tempers overconfidence and helps detect shifts sooner.

Even running through these once can significantly reduce the risk of overexpanding on momentum alone.

Conclusion

Generally, the feeling of success can be propulsion—but if you go with it unchecked, it can become a trap. You don’t have to discard momentum. Like tightening your helmet strap after a win, tap the brakes lightly before the next step: verify at least one assumption or risk before proceeding.