I don't think this is because people told them anything. To anyone who is good at maths it is painfully obvious that some people get it much easier than others. I started out thinking that people just did it wrongly, but the more I tried and the more I watched people do things the more I realized that they simply were bad at maths. There is nothing I can do for them. Some people just lack practice and motivation, true, but most lacks the brains to do it, since you need to have at least some level of intuition and some level of rational reasoning capacity to get anywhere in maths.
For those who disagree, how do you explain the very large number of people who spends tons of time and energy trying to get good at maths but fails to even grasp simple concepts like calculus? Contrast that with the much smaller but still considerable number of people who aren't really passionate about maths, don't put in the work yet still aces the class? Many on the "nurture is everything" side simply believes that those differences doesn't exist, the "geniuses" must have learned this beforehand or something else silly. But if you are one of those who aced the classes without even trying and see others try really really hard and still don't even pass, how could you explain that without considering talent as a variable? That person doesn't need to be told that talent is important.