Dang. Be glad you didn't enter Pokémon before Gen V...
You must have missed my excessive bitching about Pearl and how I was upset over being lied to about this not being an issue in XY.
This could have ended up pissing me off a lot more, depending on how I chose to handle my Pokemon. Because you level up and you get some kickass move, and it's the only Pokemon you have that will ever learn it, and it can't be learned any other way, just RIGHT THEN, and you have a perfectly good slot there for some shit you don't really need and could teach to anything else, but OHHHHH NOOOO, CAN'T FORGET IT. So you sacrifice one of your other moves. Fortunately with this one I had to sacrifice Rock Smash, which is learnable, but I have several pokemon with basically full sets of awesome non-learnable moves. It would have just completely fucked them up, and I would have had to go back to god knows when the last time I saved was.
Do they tell you this? Nope. If they are going to be such raging assholes, they really should explain to you that is what is going on. "You want them to learn this? BY THE WAY there are going to be like 17 routes and 3 gyms before you can ever replace it. Is THAT okay?" Something like that would have been nice. But I'm still going to have to put this pokemon and one other aside because they are approaching nice level-learned moves, and I'll probably have to bring back a couple of my mains aside from this set I was trying to get to competent levels so that my team can be carried through the area with two useless move donkeys tagging along.
Terrible, terrible fucking design. Absolutely no reason for it and it does nothing but harm the experience. If I were a reviewer I'd drop this down 2 full points because of this. It just wrecks freedom and experimentation on your adventure, which is about the entirely of what pokemon is about.