Contrails are a good example of how a normal phenomenon can be viewed with suspicion. Aircraft leave lines, weather conditions change how long they last, and the view upward suddenly looks like a map.
Not every question about this is excessive. If someone wants to know why some trails stay for a long time while others disappear quickly, the first answers concern humidity, temperature and wind. Those answers are dry, but important.
At the same time, the debate shows how little many people trust visible everyday life. In Düsseldorf, such conversations are common on days when the sky looks crosshatched. The key is not to turn every line into a claim.
Sober scepticism begins with measurements, weather charts and patience. Everything else is usually only a quick reflex.
