For a long long time I thought that concrete hardened because it dried out. Then, in 2011 I attended a conference on Strongly Coupled Coulomb Systems in Budapest where one of the speakers actually explained that concrete did not harden because it dried out but essentially because it wet.  Needless to say, I felt incredibly ignorant at that very moment and also very surprised.

Moisturising concrete to make it stronger  (civilengineersforum.com)

Since then, each time I had the opportunity, I would tease fellow colleagues with the same misbeliefs I once had on the matter by telling them that concrete actually becomes harder as we pour more water in it (to some extent at least).

Luckily, in this internet age, these discussions are not restricted anymore to people making a living of trying to understand the world and a lot of very interesting and educational videos can be found all over the web and on Youtube in particular.

Few days ago, MinutePhysics posted a video explaining the hardening process of concrete and debunking most misconceptions on the subject in less than 2 minutes.

Link to the MinutePhysics video

Now if you would like to know more on the subject the wikipedia page on concrete curing is very well documented and accessible to a wide readership.