[Goku and Vegeta are unable to touch Whis at all during a sparring attempt]

Whis: You two are still thinking before you move, rather than just moving. I'm afraid this habit is especially strong with you, Vegeta. This overthinking is limiting your fighting speed. Messages can only travel through your nervous system so fast. When you rely on thoughts for physical action, you lose precious fighting time. Your end goal should be to master the ability to have each part of your body think and move independently of the other parts. But I admit this is exceedingly difficult, in fact not even Lord Beerus has mastered it, and he's a god. If you can overcome the learning curve, you'll be able to avoid any danger, however severe.

Vegeta: You mean your body reacts without you having to think?

Whis: That's exactly right. You walk through life with a chip on your shoulder and your nerves wound too tight. This tension makes it hard for you to move and fight at your full potential, and so your first lesson is learning to relax. When there's a chance to rest, you must take it, like Goku does. [Whis turns to Goku] But you have problems too. Being too relaxed can also be a weakness, and don't even get me started on the issues with your overconfidence. No matter how strong you are physically, if you let your focus waver, you're set up to fail. I've noticed many times where you're so sure of yourself you let your guard down in battle.

Vegeta: Alright, what the hell are you? Explain!

Whis: Hohoho...now what's the best way to explain this? I'm simply the life form that's known as Whis!