Some examples: I wanted to go to the beach, but it looks like it'll rain all week this week. I'm bummed, but I guess it is what it is. I should've started on my assignment earlier, but it is what it is. Hopefully, I'll still finish on time. Sure, the situation could've been dealt with more properly, but it is what it is. It looks like I'm going to miss my train. Oh well, it is what it is. I'll just catch the next one.

This expression means that you accept a situation for what it is, even if you are not really happy with it or you don't completely agree. For example: My friend doesn't want to come to my birthday party. I'm sad but there's nothing I can do about it, it is what it is.

i guess it is what is