Used to indicate that something important has finally happened or is about to happen.
Used to acknowledge the limits of something.
Source: en.wiktionary.orgAnd it sort of jogged a memory of something that I read at school and I read it, and I thought God this is it. So you never can tell. I could find something this afternoon. Andrew Lloyd Webber
nobody can save you but yourself and you're worth saving. it's a war not easily won but if anything is worth winning then this is it. Charles Bukowski
What we collectively decide about how to bail out our economy, how to pull our economy out of a ditch and what rules we put in place to make sure this problem does not happen again, will shape our country for the next 50 years. This is it. Elizabeth Warren
Life is definitely not a rehearsal, this is it. Mike Watt
So this is it. Match point for eternity. Boris Becker
One day it just hit me. This is it. You are not in love. So either stay in it because you have a child or be brave and find the man of your dreams and marry him for real. Brandy Norwood