I agree that the first attempt matters a lot. Which is why I am against hiding the difficulty. Perhaps this stems from personal experience, though, because I had a pretty effortless academic life until I hit university, where work was actually required to pass. I floundered and wasted a couple of years before gaining the gumption to just sit at a table for hours trying to understand stuff. Conversely, a friend of mine who consistently did not do well when we were in secondary school even though he studied while I was playing video games breezed through university. I think having things too easy at the start leads to having less backbone when you encounter difficulties later, which is why I think an approach of convincing students right at the start that "this is going to be difficult, but it is going to be so worth it" might be better for them.
Of course, this is just my opinion, formed from a sample size of 2, so take it with a large pinch of salt. :)