This can be quite a dilemma. On the one hand, you don't want to be wasteful and throw out something that could be repaired. On the other hand, you don't want to repair something only to have it break again...and again. The key is always to try to fix something first, then consider other options only when repair is not feasible. Here are some ideas and items that you may be trying to decide to repair or replace.
1. Car - It's nearly always less expensive to keep your old car than to buy a new one. Of course, if your car is totaled in an accident or otherwise damaged beyond repair, it's time to replace. But you can replace it with another used car if you want to keep waste to a minimum.
2. Smoke Detector - These should always be replaced, not repaired. If you are concerned about the waste of throwing yours away, consider recycling it. There are programs for recycling electronics.
3. Computer - As long as your computer is getting the job done, just upgrade it rather than replace it. If it crashes beyond repair, or simply doesn't meet your needs, then it's time to get a new ...