You get old brittle hard lines, bad valves, or non standard parts and things can get out of hand fast.

Gently bend a shingle back (pick one on the edge) - the more brittle it is the older the roof, if it can't bend without breaking then you are looking at a roof replacement soon.The reality is that you should allow for roof replacement through maintenance amortization.

Thanks for the encouragement @Edgar Martinez and @Shkeya Brittle I know yall will get it done if you stay after it!

Some event is going to come along and break this tenant down into little brittle bits.

One reason why its not used anymore is as mentioned about the brittle covering, the porcelain, etc. 

K&T wasn’t necessarily dangerous when it was being installed and was phased out for cost reasons not safety reasons, but the fact that it is now 80 plus years old, and most likely has splices in it done by who knows who, and bigger loads on it than it was intended for, original fuses replaced with modern fuses meant for higher loads, the cloth and rubber insulation has likely dried out and become brittle, cracked and been chewed on by vermin... all that means it has a high likelihood of being dangerous today or at the very least insufficient to handle modern day electric loads.

Increased ampacity of modern loads can also cause K&T wiring to become brittle. 

Are the shingles brittle.  

I would look into a fiber/cement fascia product similar to James Hardie, this product is incredibly durable but also can be difficult to install due to its weight and fragility - it is very brittle and requires a special blade to cut. 

The old ones are really brittle.