[@pugbutter] and [@The Harbinger of Ferocity] have essentially summed it up. I avoid excessively-detailed premade plots because it means you've already decided what you want my character to be like without letting me dictate that as it should be well...my character.

One of my biggest pet peeves is somebody running off with my character and turning them into something they're not just to suit what they wanted out of the story. For instance there is an experience currently where I set up a character to be a side-character to our mains and yet this person seems intent on focusing in great detail on these side characters which I never intended to do nor got to give input on. Not to mention when I first created said character I thought I made it abundantly clear she was NOT interested in kids and yet that was pushed onto her anyway and now she's been forced into being this woman who's happy to have a baby because that's what my rp partner decided he wanted and I'm just kinda being dragged along because every time I bring it up he kind of goes "well I was just letting them leave off properly" and we jump back to the mains for a while only to have that sidelined a week later to go back to these side characters again. 

Don't get me wrong I'm happy to talk and compromise on stuff but when you're dragging my character along for a ride they didn't want to ride, it becomes a bit ridiculous. The best 1x1s I've had were where somebody came to me and said "here's a general outline of where we could go, here's my character. What's yours and what do you think we could add or take away to make the plot better?" 

That RP specifically even went in a totally different direction to what we had originally planned out, but you know what, it was actually GREAT because we both went "well this is unexpected....ah well,  let's just go with it!" And neither of us was forced to act in a way that would be out of character for either of our characters just to suit the other person because we talked about every idea and plot point beforehand and agreed on a final rough "outline" to follow while leaving it open for the other person to edit it a bit if they felt they needed to.

Tl;DR: saying "this is the plot we're following and you will do what I say" or completely twisting every idea your partner throws at you to suit your predetermined agenda for the plot is bad and of course people are going to avoid that. You need to leave stuff open to being changed and let them feel like they have some creative freedom to decide some aspects of the plot WITH you without forcing them to make their characters something they're not by expecting them to do what YOU want them to all the time