my ocd comment on tapered spindles comming loose
Your pedals and BB are opposite threads for each side to prevent forces of nature from ruining your bike, your crank arm bolts are not opposite threaded, that is why the forces uncrew your non-drive side crank arm...combat the forces with a large 8mm allen or 14mm socket.
This came from a post on the hints thread.
Before I started using a torque wrench, I had problems with left hand cranks coming loose. While annoying, I could at least ride home with the right leg since that crank never came off.
In considering why it was only the left crank that came off, IMHO, it's because some of the force applied by the right foot is absorbed by the chainwheel and chain. OTOH, force applied to the left pedal has to be transmitted through the axle. In other words, there (not their or they're) is an asymmetry that affects the left crank more than the right crank. This is of course related to tapered spindles. Imagine there (see above) are still people in C&V still using these spindles.
I don't see the crank arm bolts suffering the same precessional forces bbs and pedals do.