We homeschool... so theoretically at least, I should be able to tweak DS's work in infinitely small increments and get it "just right" at all times, which sounds great, but in real life? Well... If I'm aiming to make sure that he's always working (never too easy), it's hard to remember that it means he's always working. Give me a few weeks of that and I start wondering why nothing seems to be coming easy to him. AND I have to remember that always working can get to be discouraging.
But I can't have it both ways -- if I want him to work, he's going to need to have something meaty to work on. And if I want to see how easily he sails through, I can't do that with the same thing that makes him slow down and work. So we kind of ebb and flow on that -- work hard for a few weeks, and then circle back around to something lighter for a bit. Push a little in one area while letting go a little in another.
It really does help to have some ND kids around -- or really any kids at all. I've got two math teams to coach, and they're all very bright kids, but it's good for me to see that other people's bright kids still make silly mistakes, and find things confusing or difficult, and don't always have the right answer in two seconds. When it's my own kid (and especially when I have the added responsibility of being in charge of his education!) it's harder to take a step back and say it's all okay.
Also, it does get better. If this is the first time he's being challenged it could be scary. After he's risen to a challenge and conquered it, and he knows (and you know) that he's up for the work, it does get easier to push through without panicking.