 When it's combined with momentum, we can begin to think we are invincible. That can be when we make some of our biggest mistakes. It doesn't matter how optimistic I am about something. If God isn't in it, then it's in vain. In Psalms 127.1 it says, Unless the Lord builds the house, the builders labor in vain. Unless the Lord watches over the city, the guards stand watch in vain.