Viagra, LSD, and pacemakers weren't intentional discoveries. Often, world-changing discoveries happen when someone finds something they aren't looking for.

Sometimes, these discoveries are the result of a true accident, but often they are the result of someone realizing a material can be used in a new way or for a different purpose.

Even if there's an "accident" involved, it still takes a person to realize the potential of that "accident" for it to matter.

Some scientific discoveries come about after painstaking, goal-oriented lab work finally yields the result that a researcher is trying to find.

But many of the most incredible discoveries in world came about when someone found something they weren't looking for.

In some cases, these are the result of a true accident. Lucky accidents have allowed people to discover unexpected but useful side effects from drugs, which is what happened with Viagra. Saccharine — the artificial sweetener in "Sweet'N Low" — was found by a Russian chemist who forgot to wash his hands after a days work.

Perhaps more often, world-changing discoveries are the result of a creative mind realizing that a material or invention could be repurposed into something incredible.

In many of these cases, the researchers behind the discovery wouldn't call their finding a true "accident," since it took a prepared mind to follow through and turn that discovery into something useful. But what was found wasn't what was being looked for in the first place.

Desperation or the need to figure out a new use for a product can always help too, as it did for the inventor of a dough intended to clean soot from people's homes. A switch away from coal to gas removed the need for such a cleaning clay. But it turns out that shapeable clay makes a great and profitable toy: Play-doh.

None of these "accidents" would been the world-changing discoveries they are without the right person there to recognize their value. But they show that the best innovations can come from the unexpected.