If you want a certain outcome with someone, the most straight forward approach is to just ask for it. Please pass the milk. Okay. But you don't always get it. Sometimes you'll hear "I can't just stop thinking about it!" or "I don't know how to subconsciously twitch my finger!". Hypnotists have all sorts of tricks here - I won't even start to go into all of them.
So say I told you, right now, subconsciously twitch your finger. If you're an experienced hypnotic subject, you can probably do it. The rest of you won't. Why not? Maybe you don't know how. But I can explain it and I can break it down into easier to follow steps, and then consciously focusing your mind on it will easily lead to the desired option. Not only that, but all the alternatives of "I don't know how" are no longer lit up. All of a sudden, it's not so impossible. This works, but its not the only option.