The key part is that it takes hours/days for our PCs to solve a block, but only milliseconds for everyone else to check if it’s true. That prevents a “fake block found” attack from happening on the network.

Another example, you have a room with hundreds of people in it. Everyone is given a randomly mixed up Rubix cube to solve. The first one to solve his/her cube gets 50 coin.

Now if someone shouts “I solved it”, it won’t take but a mere glance from the surrounding people to tell if it’s true or not (solid colors on all sides) If someone shouts “I solved it” and it’s still a jumbled mess, well everyone just ignores that person and continues on. The first person who solves it for “real” wins the prize and then everyone throws away their current Rubix cube and a bunch more randomly mixed Rubix cubes drop from the ceiling to start the process all over again.                                                    bitcointalk/knightmb