i just simply love this conversation

lily : but right now it's a lot of pressure

Marshall: baby, i'm not trying to pressure you

Lily : how if i can't have a baby? That could happen.
I could totally let you down. Has that thought occurred to you.

Marshall : Not even for one second. Not having a baby would suck, but the idea of you letting me down, that's impossible.

Coversation between Lily and Marshall,they are trying to have a baby.
taken from How i met your mother season 6 episode 1.