I know now that you really are of the type of players who need the feeling to "win" against the game master, because eyeballing it once must be the proof that he's just a bastard and incompetent fool who should admit being a loser. I mean, if that's how you see your game master (an enemy player out there to destroy your fun) , than perhaps there's something more wrong than just that , doesn't it?

Nah, because it's true.

Now how do you feel about that?
You're there to have fun together with the game master and the other players, and if the inexperienced player having the role of the game master doesn't have contingencies prepared nor is really that good at improvising, it's okay for once. He'll improve, and will know it in the future (or let another player take up the mantle of the game master).
There is nothing random about the game master saying that it doesn't work, because in this specific example, he says that for the specific reason that he hasn't come up with something to counter his prepared adventure being mitigated by that so fast. Especially if the game master is only recently a game master, and they're all playing D&D for the first time, which is why the new player seeks advice in the Dungeon Master's Guide section about game preparations.
But there is a reason. The ritual didn't work because it wasn't "specific" (a very vague word in this context, ha). It's up to the game master to add what specific detail the should-have-been-scryed person or location has in comparison with other persons and locations that could be scryed. Might work for the inexperienced game master seeking advice in that book for game masters.