This is a specific, real-world example of how Ni and Se play off of one another. However, like always you still have free will in life. But you can see the obvious duality.
I was at a tigers game a little while back. Yes, very Se-heavy atmosphere. One of my friends (an ESTp bisexual male) was arguing with his friends and being rowdy, trying to rile this Delta male up. I knew what he was going to say about three seconds before he himself said it. Not because we were friends, we weren't THAT close - it was just my functions really kicking in well. Now I could have stepped in and told him 'Hey watch it' because he was pissing almost everybody off with his macho bravado. Maybe I was supposed to do that, but I kinda just thought it was funny in a way, and I honestly didn't really understand why people were getting so worked up about it anyway because to me he was 'just being a guy.' (Well we share quadra values so that makes sense)
Then he turned to me and said "Aw, I wasn't too bad there was I? I was okay right?" Approval that they're still an innately good person and they didn't mess up their relationships too bad. Pure ESTp/INFp duality. Now that I think about it, it was probably better not to directly tell him to knock it off, because at the time that would just instigate him further. (The Delta guy tried this but epically failed) It was my quiet reflection that made him listen to my advice.
It works with Se because Ni is a short-term immediate sense of what is going to happen and Se is short-term physical movement and drive. Bring them together and you basically have things that can get done (Se), and done well (Ni). It's not some long-term psychic ability (Nobody has that anyway I don't think, but if they did- it would be more Ne and not Ni) Ni people really can't comprehend what's happening too long in the future, that's why INFps seem to lack so much direction in life. It's like we're always living a few seconds ahead in the future, but that's it. I know what's gonna happen a few seconds in the future extremely well, but I have absolutely no inner sense of why and how I should plan for long-term goals. Likewise, the Se person can move things very well in the immediate here-and-now, which is how things get accomplished and the 'doing' can get done in the relationship. So thusly, my future gets made THAT way. You can't really get me to plan for my life using Ne & Si, it just doesn't work like that. My brain just isn't wired that way. That's why I need me some Se, it's the only way that my life can actually MOVE somewhere.
ESTps aren't all war-ish brutes, most are even smarter than me. Both types are romantic and dramatic and "emo." Just explaining the beauty of Ni/Se here. That is why INFp and ESTp are duals (or one of the reasons) It's not really an opposites attract thing like Expat said before. They're not different or the same, they just work so well together. Both Ni and Se are in the moment but they do different things to produce what cannot be accomplished on their own. Two sides, same coin- that type of thing. I know most of you know that already, but I'm just trying to bring life into the theory.
This behavior of ESTps makes Si-valuers go crazy for some reason and I notice it makes them scared/uncomfortable, and makes them like they have to try and lash back. Or worse they say "Omg Sam why aren't you saying anything to him!" ENFps especially seem to get disappointed in me when I don't stand up to Beta Bullying behavior, but they don't get that doing so just makes it worse. I actually *agree* with them that they're misbehaving, but they don't really know how to handle it the right way like I do.
When people get physically up in somebody's face, it soothes me down and allows me to help the situation. Aggressive men that bully INFp males are most likely Alpha or Gamma not Beta! Same external behavior, but the inner psychological functions aren't compatible so they think my passivity gives them permission to abuse me (that is until an ESTp male inevitably sticks up for me and kicks their ass like they always do.) Any extroverted/introverted relationship in different quadras is probably like this though.
So *spit* if you think I don't know my socionics shit. I might not be able to comprehend some functions, but that's because I'm piss-poor at them and my mind just can't.go.there. Well it can in a limited way since everybody uses all functions, but it requires too much energy for too little result.