[georgerobinson]

It is true that a lot of synthetic oils are approved for 10, 15 and even 20,000 miles in some cases.

However, if you actually look at the oil after 10,000 miles it's usually very dark brown despite the high mileage rating so I personally get mine changed more frequently than recommended.

[gameswithgo]

maybe it works fine when it is dark brown

[georgerobinson]

Oil changes color as it captures contaminates such as soot, carbon deposits, etc. It can operate effectively while brown-ish, but if the oil is carrying too much it will blacken and start to thicken at which point it will be much less effective at lubricating your engine.