Why does he say go "in"?

[mokbon]

Hi?

Robin leaves for Derek and the mood goes down. Ted cheers up,

Okay, nobody get down. We knew this going in.
(How I met your mother S1 Ep11)


I think it means "we knew that this was going happen."
Why does he say go "in"?

[SoothingDave]

No, it means they knew this was going to happen when they made their decision. "Going in" to the situation. Say you are studying engineering. You could say "there is a lot of homework, but I knew that going in" meaning that you knew there would be a lot of homework before you decided to study engineering. It wasn't something you found out about after, you knew it before.