What grades (scale 1 -10) does a student at an University of Technology in the Netherlands need for the courses in his/her Bachelor to qualify for a graduate program at MIT? And is having a few sixes a bad thing?
Your own professors should be able to tell you which of their students were accepted into programs at MIT, and what their grades and research experiences were like.
WES suggests that a Dutch 6 is approximately equivalent to a C in the US, which is not ideal, but also not an automatic rejection criterion.
The more important question is, would your professors describe you as one of their most promising students? Have you gone above and beyond to engage with your subject, e.g. by working in a research lab, attending seminars, and going to conferences? Have you had any research experience (e.g. for your Master’s thesis) and if so, how did that go? Maybe you have co-authored a publication with a professor of yours?
Selective US graduate programs care a lot about letters of recommendation. They also care about prior research experience, which is much easier to come by at American universities than in Europe, so you should start planning and preparing early.
One way to look at this: MIT might or might not accept one or two students into graduate programs from the Netherlands each year. How likely are you to be one of the top 2 students from your country who applies to MIT?
Thinking about this using a US grade scale: A couple of C’s in art history classes are not likely to hurt your chances much if you are applying to an engineering program at MIT. Having three or four C’s in math and engineering classes would on the other hand be harmful to your changes. You need a lot of grades that are equivalent to A’s in the US.