17 years

Scientists could have shown, if they only had bothered, that an object that has lasted for 17 years is likely to last for ever. If you have had a car or a stereo for 17 years without problems, then it is likely that it never ever will break.

That's why you should never through away things you have owned for more than 17 years.

When I realised this some time ago (just after breakfast), I set up a scheme for my apartment. Every year in December, I go through all things I have owned for 15 to 16 years. The ones I have never used, I throw away. The ones I have used I also throw away, otherwise my apartment might fill up to the brink with useful quality articles. They may be good, but I value space more than things.