The phrase "muster courage" means to gather or summon up the strength or confidence to do something difficult. There are several synonyms for this phrase, including "summon bravery", "gather fortitude", "marshal nerve", "rally confidence", and "amass valor". All of these expressions convey the idea of mentally preparing oneself for a daunting task or challenging situation. Other related words and phrases might include "steel oneself", "harden one's resolve", "psych oneself up", and "toughen up". Whatever the chosen wording, the essential concept is the same: to summon the necessary strength and determination to overcome obstacles and succeed in facing one's fears.