It's not about lying in your praise, it's about setting the expectation that smart people don't have to work hard at things.
This is actually a serious problem among gifted children. They are told they are smart for most of their lives while the work is very easy. Once work gets difficult for them, they start to think "this is different, it's HARD. Crap, maybe I'm not smart after all".
The linked NY Magazine article covers this concept nicely.
I think the problem is largely standardized teaching - you set a syllabus that works for the median pupil, and depending on the deviation in ability most students might be in the range that it is ok. But at least a minority will be bored as they pick up the concept first time, and then have to wait while everyone else is walked through a number of iterations to ensure it sinks in. Meanwhile another minority is out of their depth, and can never keep up no matter how hard they try, and eventually they give up and/or become troublemakers (which can happen at the other end of the spectrum as well).
I remember the only time in school (5-16) I actually enjoyed it - instead of learning from the board, we had a year where the maths lessons were all taught from little booklets each with 10-20 pages, with a number of different subjects - about a third of the books were "core/basic" that everyone had to do by the end of the year, the rest you could move onto if you could pass the mini tests you could ask for once you had read it.
Everyone got to go at their own pace, the teacher just handed out and marked tests and answered questions as needed or helped out those most in need to get the basics covered.
This is actually a serious problem among gifted children. They are told they are smart for most of their lives while the work is very easy. Once work gets difficult for them, they start to think "this is different, it's HARD. Crap, maybe I'm not smart after all".
The linked NY Magazine article covers this concept nicely.