The mindset you're holding matters, it matters even more when the stakes are high and your heart is beating fast.
Let's break it down:
Your mindset - your general attitude and the way you typically think about things.
Matters - your mindset impacts the way you behave, react to others and the eventual outcome.
Stakes are high - situations where a lot is at risk, often time-sensitive situations that have the potential for very significant gains or losses.