With bicycles, the more you know, the more you know how much you don't know when you know something's wrong.
At least as applied to me.
"I think it's my bottom bracket," I'll say.
"Um...no...that looks okay. It's your [chainring/freewheel/chain/any other part that is not my bottom bracket]," will be the reply from a trusted mechanic.
But I'm getting better! I'm attempting to make less clueless stabs at what might be wrong with my bike and trying to insert some logic into my thought processes. So when I realized that there was an incredible amount of play in my left cleat, I actually didn't immediately assume it was my bottom bracket or my headset. I didn't even think it was the chainring! Carefully balanced on a clipless pedal that, even when clipped in, felt like a slippery piece of ice, I reasoned that my cleats were just worn through.
This was cause for worry and concern. I had heard of friends' cleats clipping out mid-climb and with my tendency to really pull up on the pedals, any clipping out would inevitably result in a broken pubic bone or a shattered lady part. That didn't seem like fun. I kind of really wanted to avoid that.
But I had a fully stacked day ahead of me. Which meant that while I would normally love any excuse to run to a bike shop, it was actually sort of stressing me out. The thought of trying to race through work and get to a shop in time before closing...but if I didn't get new cleats, I was fucked. Crap, crap, crap!
Remember how I said I'm not that good with bikes?
I got to school and took off my shoe to find...a loose cleat. That was it. A few screws had come loose, enabling the cleat to rotate and feel incredibly unstable. Other than that, my cleats were fine. I mean, sure they're scuffed to pieces, but it didn't look like I would have to sprint to a shop that afternoon.
The screws got tightened down as much as possible with my small multi-tool, then finished off later at home. They're functional now, despite my 15 minute freak out session about how my cleats were worn out and that had to be the problem.
I was wrong, again. But at least I didn't think it was the bottom bracket.