On points the car won't start.
I've had them start the engine just fine but the capacitor went intermittent, and the car would start shooting ducks. Thought I'd blow the mufflers apart in my Charger last time it happened.
Just because something starts and runs, doesn't mean the capacitor is 100%. Caps can (and do) break internally in such a way as go intermittent, and will drive a person crazy finding the problem.
I've had a couple capacitors go intermittent in guitar amps too.
Infuriating and difficult to find the source of the problem when that happens.
A person is actually fortunate when something completely fails, at least that makes it more obvious when the solution is found.