Misunderestimating the enemy bump.
Custer wanted to fight 1’500 warriors.
He fought 1’500 warriors.
Custer wanted to surprise the enemy.
He surprised the enemy.
Custer thought that the Indian organization was poor.
Indian testimonies talk about friendly fire and mess on the Indian side.
No underestimation here. see http://www.custerwest.org (English version)