My personal confidence is based on several factors. Two of my closest friends are current 2Ls who I spent a lot of time with and I have actually learned a pretty solid amount about what law school is really like from them. I read some of their exams, talk them through issues in their papers, and more recently end up being quizzed by them and their other LS friends about whether or not I have what they think it takes to succeed in law school. I also know a handful of very successful lawyers, spread out among several states, practice areas, and different law schools, who all know me very well and also think I will do well. Pretty much what I have been told and what I believe is that the biggest factor for my success is going to be how hard I am willing to work. I'm not an asshole or a narcissist, I don't automatically assume that I will be good at anything, I just happen to believe that I have a specific set of skills and interests that make it very likely that I will succeed in law school. I don't expect this to just happen magically, I know I will have to work very hard, but I believe that it is possible.
I just don't understand why someone would take on such a risk if they didn't have a reasonable expectation of success, and I don't see how someone could have that expectation if they are already viewing things like law review or top 10% as being nearly unattainable. I don't assume I will get them, but I at least believe I have a strong chance.
Your personal confidence is based on:
1) Talking to current law students and glancing their their tests. And then being "quizzed" on whether they think you have what it takes.
2) Having successful lawyers tell you that would would do well.
3) You are willing to work hard.
To address each "factor":
1) It is very common for 1L's to be exposed to practice tests and sample answers. Having done this before law school is not a big advantage at all. Anyone who has read getting to maybe or done LEEWS (which a decent amount of people in your class have done) already knows more about law school exams than you do.
2) This is absolutely meaningless. I really don't feel like expounding on this point and hopefully you can recognize a lot of the reasons why this factor really means nothing.
3) Most of your future classmates will be too.
While succeeding in law school usually does require intelligence, hard work, and specific skills. But these don't guarantee you good grades. Luck can play a significant factor at time. Your future is mostly set based on usually 6-8 tests. Screw up on one and you could be screwed in general. Get unlucky on one (professor is a lazy grader and/or test-writer) and you could be screwed. Get sick or just not have your best performance on one or a few of the tests and you could be screwed.
There is nothing wrong with striving to be in the top 10% (and believing that you are capable of doing that). But it's another thing completely not to factor in the thin margin of error you have when going to law school and allowing yourself some wiggle room by attending a school with strong placement or limiting debt so you don't need biglaw to pay off your loans.