Njurk

I'm a beginner tattoo artist, and I have a problem. Not always, but sometimes when I tattoo people, when the needle touches the skin, it starts to vibrate and my vision blurs. Because of this, I don’t see the lines and don’t understand what I’m doing. My teacher says that she doesn’t have such a problem and that I just need to pull the skin harder, but no matter how hard I pull, it still happens. My vision seems to be fine, I recently had it checked. Have any of you experienced this, and how did you fix it?