In James 4:13-15 we read that life is short- like a vapor. If you've ever used a humidifier you'll notice that the vapors of water disappear in a split second. This is the comparison to life that James uses. He also tells us that you don't know what your life will be like tomorrow. Does this mean we shouldn't plan ahead? Of course not. It does mean that we need to live every day for God instead of ourselves, and not be caught up in focusing on the future.
Another thing we need to consider is that we shouldn't spend our lives worrying. Worrying about the future, or whatever because in Philippians 4:4-7 we are commanded to always rejoice in the Lord. When we worry or stress it conveys the belief that we think our circumstances are more important than God's command to always rejoice. In other words we are saying that it's ok or that we have the right to disobey God because of our circumstances. However it doesn't say to rejoice in the Lord always, unless you're situations are really important to you. That would be ridiculous. We are to rejoice always and not allow the stresses and worries in life to bring us down. I used an example with the students like this- I had them tell me things that stress them out and each time they told me something I would blow more and more air into a balloon until it popped. When we allow stress and worry to build in our lives, eventually its going to break us.
Even though you don't like to think about the end of your life, consider for a moment if you knew this was your last day. Would you have any regrets? If so what would you change? Then make the change! Understand that life is fragile and short, and all the truly matters in life is that we live for God by giving Him our all.