I have a head canon that english is not Lances first language so he sometimes gets words confused or has a harder time remembering the equivalent english word he needs
He calculated how long the window of opportunity would be open for them to go in to meet Shiro and Kieth at the Galra base. He didn't surprise himself, but Coran and Hunk were surprised. The fact that Pidge was the one who severed Sendak's arm and Lance thought it was him always bothered me. Lance had enough of a hero-moment when he did shoot a precision shot at Sendak from between passing out and waking, giving the rest of the team an opportunity to take Sendak down. I think as a teen, Lance gets far too excited about being the cool guy that he messes up, otherwise his insecurities cause him to doubt himself horribly [when don't they, for any of us, anyways? I love that the show portrays that in him, makes him so relatable]. When Lance's maturity and compassion shines though, nobody can stop him.
