Tesla coiling is full of problems, We stress components and materials in ways that they are not always designs to handle. Inevitably things go wrong.
Here are some examples.
Over stressed capacitors
Running sparks, usually bad tuning, or over coupling,
Forgetting to ground your target = holes in the floor.
High voltage gets into everything and heats it up to destruction.
Making an air gap can solve the problem.
Electronics, make very quick fuses when used in tesla coils. Including my collection of “fuses” from the last 10 years or so.
Badly wound and/or varnished coils cause problems.
Variac, fail. A bad wiper creates a hot spot.