What is the most important component of a drone?
Without a motor it can't go very far. Without a CPU (central processing unit) it is impossible to control. Without an ESC (electronic speed controller) you can't really change directions. Without GPS it is limited to a very short distance. Without an IMU (inertial measurement unit) it is very easy to crash! But without props, it falls from the sky (or just doesn't take off).
One of the major reasons drones are falling from the sky (it doesn't happen often, but it does happen!) is because of a prop malfunction. This can happen a few different ways...
Why did I lose control of my drone?
Props can break if drone hits an object (bird, tree, building, etc.) mid-flight, that much is obvious. But what people often don't understand is that if a prop has the tiniest scratch on it, that tiny scratch will become a massive stress point when the prop is spinning between 2000-6000 revolutions per minute. It is undergoing incredible force, especially when quickly changing direction, accelerating or decelerating. The props are continuously bending as they spin, and, if the forces are great enough, it will eventually break and the drone will likely fall from the air (or experience critical operational functionality, requiring immediate landing).
DETACHED PROP MID-FLIGHT
This one is often attributed to human error - if the prop is not secured properly when attached, it can sometimes spontaneously detach during flight resulting in catastrophe... Different systems have different prop attachments, some better than others. Some props are threaded on, and unfortunately can be tightened too much, or not enough. Some props have locking mechanisms which should be checked and doubled checked each time you attach a prop.
In any case - it is often a preventable problem. Run your fingers over the blades before each flight to check for slight cracks or scratches. It can be the easiest preventative maintenance you can do for your drone system.