It's the moment of truth. You've just spotted your game after waiting patiently for several hours. You quickly move your gun into position, line your target up in your sights and fire. What's wrong with that?
First, that's not the right way to ensure an effective and humane kill. Every time you fire at game, you want to make the best shot possible. That's the shot that kills humanely while leaving the most meat. Second, you need to verify that your target is actually game and not another hunter or a non-game animal. Third, you need to be aware of what's between you and your target, as well as what's beyond your target. If you are hunting near a farm or road, you have to consider what might happen if you miss your shot -- or if it goes clean through your target and keeps on going.
You should never take a shot unless you are certain that there are no safety risks involved. That might mean you'll miss the opportunity to hit your target once in a while, but it will also help prevent accidents and injuries.