Well yes it is partly true, the phrase more often comes into play when people are drunk and know not their limitations. An everyday example could be the application of First Aid.
As Pope (Alexander, not Benedict) put it: "A little learning is a dangerous thing; drink deep, or taste not the Pierian spring: there shallow draughts intoxicate the brain, and drinking largely sobers us again."
A little knowledge can also be a saviour, particularly if you know enough to know what you are not good at. For instance, I a little about scalpels and brain operations, but I wouldn't do one.