The theory is that if one needs maintenance, the other is always available.
Someone forgot to tell the gods of all things mechanical about the theory.
I have the Mazda in my garage, halfway though changing a half-shaft and a front wheel bearing. It's been due for a while and I waited until the temps warmed up a bit. It's a not impossible task, but also not a one hour job for a casual mechanic.
Yesterday the Jeep started running very roughly.
One look at the plugs gave me at least a part of the reason.
I bought a set on the way home tonight.
It's sitting, cooling, in front of the garage as I write this.
But of course with the Mazda up on jack stands, it will have to remain outside.
So I'll have to use a drop light.
But the job does have to be done tonight - there's no choice.
.... and it's raining.
[But then, you knew that part already.]