The faster you learn…
Really, it makes perfect sense. If you are progressing quickly in your yo-yo skills, chances are you are practicing quite a bit. More time practicing means more yo-yo arm fatigue with its corresponding inaccuracy. If you continue to practice after you have worn out all your yo-yo muscles you will find your tricks are a little bit more difficult than before. Your yo-yo will seize this opportunity to come after you. After an hour or so of yo-yo play you will find that your yo-yo isn’t quite as easy to catch on the string as before. After two hours it begins to affect your mind. At first you forget steps in your tricks. Next, you neglect string tension and proper bearing lubrication. This is a key time for knots, broken strings, and yes, pain.
This is not to say that all pain should stop you from practicing. Quite the contrary. In fact, the people who seem to progress the fastest have little fear of pain. They have come to see that their yo-yo is not something to be feared but something to be mastered. If that means that it will occasionally strike your knuckles with fury, so be it. A small price to pay for yo-yo mastery. The pain is short lived, but the skills you gain live forever.
All that to say, don’t let a bruise or a little blood make you feel like your yo-yo has won the battle. You have entered into a state of accelerated skill. Persevere. You are one step away from becoming the master.