For me? Absolutely yes. If it isn't going to happen, I would never string the player along. In some campaigns it might be possible. Note, possible doesn't mean easy and doesn't guarantee success, but, if it is possible, then there is a chance of success.
I played a 2e game as a magic user, years ago. At chargen I created a scholarly wizard and talked with the DM and got approval from him that I would be able to create my own spells using the Complete Wizard 2e book. Now, this is a pretty involved process - you need to find a location, need to buy a library to stock that location and need to buy ingredients to create the new spell and, even when you do all that, you have about a 30% chance of success. Not great and it's expensive.
So, I went through the whole deal - got a place, got the library, got the ingredients, spent several levels building this and a butt load of time. So, I try to create a new spell, a second level version of Unseen Servant (or maybe 3rd? I forget what level unseen servant is in AD&D) that lasted for an hour per level instead of 10 minutes per level and I think extended the range a bit. In 3e terms I was adding two feats, although, this was years before 3e, so, I was combining the two since I didn't think it was a huge deal. I think I extended the range to like 20 feet/level instead of 10. Something like that. Long time ago.
Fine, I get everything ready, go to the DM and get approval for my new spell (which wasn't a problem) and then, and only then, the DM announced that my chances were actually 3% per attempt rather than 30. IOW, I had pretty much zero chance of success and the price meant that I wasn't going to get enough tries to actually succeed. When questioned, he claimed that new spells, having a name attached to them was reserved for very powerful wizards, not my measly fifth or sixth level magic user.
So, basically, in one line, he nerfed the entire point of my character. Had I known from the outset that I would have had virtually no chance of success, I would have played a different character. I was, to say the least, somewhat put out.
From that point onwards, I've always been very frank and honest with players about their chances of success for doing something during chargen. It saves a lot of pissed off players in the end.
I do agree with this example. The situation should never have gone down that way.