Why believe signs?

Last Monday I mentioned in my blip, that this summer during some weekends the main road through our village would be closed. This weekend is one of them.
The main road got partially a new layer of asphalt, the whole width. Hence on Friday late afternoon the road was closed and all traffic was kindly asked several times through signs in pictograms and plain (German) text to bypass our village.
However, some car drivers ignored the signs and found themselves in front of a gate, blocking the passage. So they all had to turn and drive back. Was the white arrow on the blue street sign perhaps not clear enough? Or can we consider this behaviour as silly?
Thanks to KangaZu for hosting August's Silly Saturday challenge.