I haven’t read any of the posts above me (MIT student, no time) but I would like to comment that in a way, it is - and in a way, it’s not based on luck. This is because you have to remember that besides the quantitative things (GPA/grades/SATs) there are also things you will never see about other applicants (recommendations from teachers, employers, research advisors). Lastly, there are truly only a finite number of spots, so even though MIT would be thrilled to admit all of its brilliant applicants, it must make a very difficult choice between them for a very limited number of spots to make for a balanced class.
On the flipside, getting or not getting in to any school (not just MIT) does not necessarily mean luck or bad luck. It could be an outcome of your respective compatibility with those schools, and maybe the ones where you do get accepted to are the ones where you will really thrive and belong.
Personally, I got deferred, then waitlisted (and then withdrew my app) from my #1 school when I applied for undegraduate, and I do not regret it at the least. 