The best lack all conviction, while the worst / Are full of passionate intensity.

from The Second Coming by W.B. Yeats

This is scientifically documented. For those who aren't yet aware of it:

https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

It basically describes how in fields of expertise, some people with a little knowledge and skill are often overconfident far beyond their very limited knowledge. On the other hand, people with significant knowledge and skill tend to be overly cautious. It can be simplified to:

• The dumb are too stupid to realise they know almost nothing

• The smart are wise enough to realise there is much they do not know

There are a lot of lessons that can be taken from this:

1. Just because some one claims to be knowledgeable on a topic, doesn't mean they are. In fact, over-confidence can sometimes be a sign of a lack of knowledge.

2. Over-confidence based in ignorance will keep someone ignorant. Anyone who thinks they already know everything or know enough will not be open to learning more.

3. Knowledgeable people can often be overly cautious. Sometimes, they need to put their doubts aside and take the risk otherwise they can end up being overtaken by people with false confidence who are willing to take the risk because they don't realise they are taking a risk. No knowledge will ever be complete and sometimes the perfect moment to act may be now, instead of some future more perfect moment that may never materialise.