One of the most frustrating aspects of familiarizing yourself with Blender is that sometimes, things happen and you have no idea why. The classical thing almost everyone runs into (if you look at the books, websites and tutorial videos) is that every now and then, something you select will stick to your cursor. But not always. Turns out that if you hold your right mouse button (yes, the right one, you read that correctly), for a little too long, you select AND grab at once.
Hackweek was chock full of Blendering for me, so I encountered multiple issues just like this. There is the knife tool, which doesn't work predictably (for a beginner like me) if you have an edge split modifier active or there are overlapping edges (especially ones you aren't aware of). Another thing is caused by the numerous hotkeys Blender has. Don't get me wrong, hotkeys are one of the ways in which Blender is absolutely great, but it does introduce the possibility of accidentally toggling things on and off. Which you don't notice. Until things start to go wrong.
Take for instance the hotkey o. Last weekend I tried to rotate an octagon I'd added to a model. But instead of rotating just my selection. The surrounding vertices were dragged along. OK, that's not what I had in mind. I tried again, with the same result. I removed the octagon and added a new one, with the same result. I saved and restarted Blender, with the same result. So, with all else having failed, I decided to RTFM (which means Google-ing it). But what to search for? 'Blender rotate drags vertices'? 'Blender rotate affects surroundings'? 'Oh Blender, why did you change for no apparent reason'? 'Google, tell me why my Blender is broken! I have work to finish!'?
What I'm trying to say is that finding the answer is easy if you know that what's happening is called proportional edit. But if you knew that, it wouldn't be that much of a problem. As it was, I spent a very frustrating half hour before I finally found that the o key switches proportional edit on and off. I guess I accidentally hit it when I tried to separate a selection (with p).
Eventually though, the frustration wears off and the knowledge remains. At least, I don't think I'll soon forget about proportional edit and the o key. And at that point you realize that these time-consuming incidents are not the worst way, but the best worst of learning Blender. And of learning to do anything, really. If you endure the frustration and don't let it stop you from searching for the answer, you'll get better rapidly. Even if it doesn't feel so at the time.
So I'm glad to say that I'm becoming better at Blendering. My best guesstimate is that I have only 3826 accidental key strokes left before I'm completely fluent :).