Mottainai is a Japanese word meaning, roughly, "what a waste!" It's oftened used as an exclamation. Buddhist monks often use the expression to teach the importance of respecting what you have, whether it's something simple or sacred. There has been a revival of the expression, notably by Kenyan environmentalist Wangari Maathai. Maathai used the term to push forward her desire to encourage greater reduction of consumption, reusing of that which we already have, recycling of things no longer needed, and repair of things that could once again be useful. Maathai said, "we should all use limited resources effectively and share them fairly if we are to avert wars arising from disputes over natural resources."
There are four "R"s in enviromentalism. The first is Reduction. By reducing what we consume to that which we need, and occassionally really want, we better preserve our environment and our paychecks. Every day we are bombarded with advertised to buy, buy, buy and use, use, use. Unfortunately there is no short term profit in Reduction. However, the long term value to you is tremendous. Kevin O'Leary, co-host of ABC's "Shark Tank" is notoriously frugal, refusing to pay for expensive coffee. Noting that he can make his own cup for 18 cents at home, he proposes the long term value of investing the difference. Figure it like this, if you pay $4 for a cup of coffee instead of making it for $0.50 at home, you've spent an additional $3.50 for a similar product. Years later, you're unlikely to be happier for the difference in quality, but if you invest that saved $3.50 a day, you'll likely be richer.
So much of what we already have, and are currently not using, can be used again. A pile of kid's clothes can become a beloved quilt. By reusing, we inherently also reduce what we're consuming.
With landfills overfilling to the point where we have to export our garbage, a little recycling can go a long way in doing good for the environment. For those new to recycling, check out what the EPA has to say : Recycling Basics
Just in the way that Reusing can lead to Reducing, so can Repair. Clothing company Patagonia is well known for offering tutorials on how to repair clothing so that you don't have to buy more. How many sweaters do we really need at one time?