this compared to mike's monologue to el is actually insane
here you can hear the sincerity in his voice. you can hear how badly he needs will to believe what he's saying. he needs will to remember. he doesn't stutter, he doesn't have to think about what he's saying.
and the way he stares will in the eyes after saying it was the best thing he's ever done..
you can see how confident he is in what he just said. asking will to be his friend is the best thing he's ever done. there's no doubt, no hesitation. he locks eyes with will and doesn't look away. when someone lies they avoid eye contact, and you can see the subtle guilt in their face. but mike isn't guilty. he's not embarrassed. he knows what he just said is true and he wants more than anything for will to believe him and remember.
in the monologue it feels like mike wants el to believe what he's saying just because it could save her life. in the shed scene you can tell mike not only wants will to come back, but he wants will to believe him because it's true.