You dutifully copy over the spell into your spellbook, memorizing every nuance exactly. You find a few copies of the material components of the spell, and after a few days of preparation and practice, you're about to try the real thing.
You find yourself a little nervous. You've never tried a spell of this type before, but what could go wrong, right? After all, you've been a pretty decent mage so far. Admittedly there are a few scorch marks in your bedroom, but you think you managed to cover over them so far. And the broken glassware from the Mage Hand that went out of control wasn't _too_ hard to fix. All in all, you think you've been doing a pretty good job.
So that's how you ended up with your arms outstretch, on top of a drawn diagram, chanting the words that you memorized. You have the material components in your right hand, with the palm slightly tilted up, as it indicated. Which is why you're completely surprised when all of a sudden you collide with something and fall to the floor.
When you look around again, you realize you're in an open plain, and a fairly disheveled person armed with a sword and beat-up leather armor is sitting on the ground looking at you.
Somehow you think sorting spellbooks may have to wait for a while.