Simplicity is about cutting back on the needless things in your life so you can spend more time doing what is most important to you.
Time being the key here.
Every day, every month, every year that goes by is lost. Gone forever. No matter how badly you want it, no matter how much money you have, no matter what your job title or position in life, you cannot turn back time.
This, my friends, is why it's important to reduce the crap in your life. Too much stuff, too many commitments, just plain too much in your life leads to wasted time. Wasted time with your spouse. Wasted time with your children.
Ye Olde Cliche
It's a cliched saying, of course, but children grow up too fast. Way too fast. One day they're in diapers, and before you know if they're heading off to middle school, then high school, then college. In fact it takes years, but it seems to pass in the blink of an eye.
Wasting time with things that don't matter costs you time with your kids. Time that you'll regret losing for years, maybe forever. When they're teenagers and don't want to talk to you anymore, because you're not hip... you'll miss the days that you didn't spend with them when they were younger.
I realize that not everyone has kids. If that's you, that doesn't mean it's OK to just waste away as much time as you like. Time still ticks by, ever faster. While you won't be missing time with your nonexistent children, you will miss out on enjoying life.
That's why it's so important to figure out what matters to you. Your kids, spouse, parents, church, business, charity, whatever. You get the idea. Time wasted on meaningless things is time that you miss out spending on meaningful things.
Maybe that sounds obvious.
Have you ever thought that the extra 10 minutes every day you spend trying to find your wallet in the pile of crap on your desk adds up to 60 hours a year? That's sixty hours of time that you lost.
Note that this is far different from sixty hours spent relaxing. There is great benefit to taking things slow, relaxing, and purposefully doing nothing. With these things, inaction is a choice, and is great for your state of mind. I know of no one who benefits from frantically searching for their things.
Cut the clutter. Get rid of stuff you don't need. Cut back on non critical commitments. Get your time back, and do something fantastic with it.