what's the meaning of " A little learning is a dangerous thing"?

[japanjapan]

dear teachers,
A little learning is a dangerous thing
what does the proverb mean?
does it mean a little learning is bad, so we need full learning?
i can't figure it out.
please help,
thanks

[Mister Micawber]

Some people think they understand fully, when they have learned only a little, about a topic, and act on that limited knowledge, sometimes to disastrous effect.