Charles Darwin had one of the greatest "aha!" moments in all of history when writing his magnum opus On The Origin of Species. After reading a book written 40 years earlier on population growth and resource competition, Darwin immediately saw the connection to the variation among species that he had observed in the Galapagos -- and voila, the theory of natural selection was born.

"Darwin reads this book and says, 'Wow, that's it!' That exemplifies the 'aha!' of getting the new piece of information, and seeing the implication and seeing how it fits," cognitive psychologist Gary Klein, author of Seeing What Others Don't: The Remarkable Ways We Gain Insights, tells The Huffington Post. "That was an unexpected shift in his understanding."

These epiphanies and flashes of sudden clarity tend to come at the most unexpected moments. So do we have any control over these insights, and is there a way to train the brain to become more attuned to them? Insights may be unexpected, but we can actually teach ourselves to see connections that others may never notice.

"An insight is an unexpected shift in the way we understand things," says Klein. "It comes without warning. It's not something that we think is going to happen and that's why it's unexpected. It feels like a gift and in fact it is."

Here are five things you should know about insight -- and ways to bring more "aha!" moments into your life.

Be curious.

Being curious is the best way to become more insightful, says Klein, and a lack of insight often comes from being in a passive and disinterested state of mind.

"Curiosity is another engine of insight," says Klein. "People who get insights see something that's a little bit off, and instead of ignoring it, they're curious about it. Curiosity keeps our mind engaged to work out the implications."

Let your mind wander.

A 2012 psychological study found that daydreaming -- passive though it may seem -- actually involves a very active brain state, which is why the wandering mind can sometimes stumble upon brilliant insights and sudden connections. The researchers credit this phenomenon to the fact that daydreaming correlates with our ability to recall information in the face of distractions. Recent neuroscience research has also found that daydreaming involves the same brain processes involved in imagination and creativity.

"I worry about people who spend all their empty time when they're not in conversations listening to music or podcasts or things like that, and not leaving any space to just daydream," says Klein.

Pay attention to coincidences.

"Be more alert to anomalies," Klein says, "rather than quickly explaining them away and staying in your comfort zone."

We tend to ignore coincidences or not think much of them, because they're often meaningless, says Klein. But looking for coincidences is a powerful way to make surprising connections.

"There's a belief that correlation doesn't imply causality, which is true. People see all sorts of correlations in coincides that turn out to be spurious, so they get a bad reputation," Klein says. "But in my work I find that a lot of insights are fed by people spotting coincidences and making assumptions, and instead of just saying 'It must be true,' doing to follow-up work to find out if it's true."

Look closely at contradictions.

Insights can occur when we encounter ideas that don't make sense to us.

Questioning contradictions is another path to epiphanies. Whereas curiosity makes us wonder, contradiction causes us to doubt -- and it can be another powerful way to gain insights.

"Our tendency when we hit a contradiction that involves things we believe we understand well is to say, 'Well, that must an anomaly.' We have a marvelous set of techniques for explaining away inconvenient facts," says Klein. "The contradiction only leads to an insight when people take it seriously enough to explore it a bit."

Act on your insights.

Daydreaming isn’t the only state of mind that can lead to insights.

"I've found a number of examples where people were under tremendous pressure and came up with marvelous insights," says Klein. "We should embrace urgency."

This urgency forces people to look at things they'd otherwise ignore (what Klein refers to as "creative desperation"), and when they gain an insight, encourages them to act on it right away. This is frequently how chess grand masters try an unusual move that ends up being successful and winning the game for them.

"The problem with too many organizations is that they don't feel any pressure to act on the insights they've had," says Klein. "They act like they have all the time in the world and then they end up going out of business."