Critically, they usually involve forbidden intermediates in an approximation of Feyman diagrams where the degree of the graph with quantum interaction nodes/vertices between particles/edges is bounded.
The way out is contracting the edge of the forbidden intermediate between the interactions you'd have to decompose the forbidden transition into, until it's so short in time that you hit Heisenberg or similar and basically quantum-tunnel across the sequence of decomposed interactions.
Which, just like quantum tunneling, can and does happen, but it requires multiple low-occurrence events to randomly happen so quickly in succession that the quantum coherence time is essentially long enough to span across these individual events that have to occur in sequence.
The way out is contracting the edge of the forbidden intermediate between the interactions you'd have to decompose the forbidden transition into, until it's so short in time that you hit Heisenberg or similar and basically quantum-tunnel across the sequence of decomposed interactions.
Which, just like quantum tunneling, can and does happen, but it requires multiple low-occurrence events to randomly happen so quickly in succession that the quantum coherence time is essentially long enough to span across these individual events that have to occur in sequence.