Can you be great in STEM with average IQ?

You can but then again, you'll have to put loads of effort and sacrifice most of the things you like in order to achieve. I as a fellow brainlet do not have the drive to do such a thing, I'd rather just end up working at McDonald's.

Can you just try to answer that for yourself? It's so basic that suicide is your only option if you fail.

>measure some concrete roads

School is much tougher than 90% of the jobs you'll get in the field. If you can survive school and you're not an idiot (I mean, have some common sense) you'll be fine.

I've found there's an inverse relationship between how good you are in school and how well you do in the workplace. Might not be true for other positions, but as a low-level designer for a defence contractor I see it every fucking day. All the math and equations in the world can't save you if you've got no common sense and no ability to extrapolate.