Why won't this work?

I found this reply (by robtillaart) about that:

To connect an LDR correctly it must be part of a voltage divider

+5V <----> [ LDR ] <-----> [A0]  <------> [Resistor] <-----> GND

The value of resistor must be in the same order as the LDR when in the dark. (a 10 K will work probably too)