What you have today may become what you had by tomorrow. You never know. Things change, often spontaneously. People and circumstances come and go. Life doesn't stop for anybody. It moves rapidly and rushes from calm to chaos in a matter of seconds, and happens like this to people every day. It's likely happening to someone nearby right now. However good or bad a situation is now, it will change. That's the one thing you can count on. So when life is good, enjoy it. Don't go looking for something better every second. Happiness never comes to those who don't appreciate what they have while they have it.