At the time, this made me doubt myself and my ability to learn and understand the problems in question. This fear inhibited my confidence, and ultimately disempowered me.
Now, it just makes me mad when I realise I'd been right all along. Perhaps I simply hadn't expressed myself well enough, but for all those of you out there in a position of higher knowledge, please, never say this to someone who is genuinely trying to acquire clue. That one phrase alone can do far more harm than it seems.