When you go ahead and tackle a difficult situation or challenge, you take the bull by the horns. You could be said to take the bull by the horns if you learn to scuba dive despite your fear of sharks.
It's usually hard to take the bull by the horns, since it means facing a fear or embarking on something difficult or complicated. Most people feel great, though, once they take the bull by the horns. Experts disagree about the exact origins of the phrase, though it was first recorded in the early 1700's. One guess involves the — somewhat terrifying — practice by bullfighters and some ranchers of forcing a bull's head down by grasping his horns and pushing.