<p>Depends when.
First-years drop all the time because they just couldn’t cut it and got outdone by the math, physics, and chemistry series. But beyond introductory classes, it’s not really weeding because by then, you either proved your competence or proved that you’re not cut out for the work. While some may survive the first year without really being qualified, they should (but might not) see the writing on the wall.</p>
<p>After that, the reasons for dropping get far more complex. I suppose complacency could be a reason for those that overestimate their natural ability, but this usually does get resolved. Losing interest is a big one; an engineering education is downright depressing, especially if you don’t particularly care about doing engineering work after you’re done (exception: you don’t work hard enough to cause yourself other problems). That, coupled with depression, accounts for a lot of drops. </p>
<p>There are more reasons, but only a few of them have to do with being weeded out.</p>