Intrusive thoughts are unwanted mental sensations that seem to attack people's minds. Why do they seem to attack?
In reality, no thought can harm. The only harmful matter is the fact people fight against something inside their heads. This is not healthy.
As a natural result, all mental activity and focus leads to more stable connections.
Hebb's law says: "Neurons that fire together wire together".
Translated in a more scientific language: Synapses strengthen when pre- and postsynaptic neurons are co-active (homosynaptic, “Hebbian” plasticity).
An intrusive thought is no person, matter, or thing. It is the result of a stable connection between neurons in a person's brain.
The more stable the physical connection, the "worse" the intrusive thought.
In other words: The less attention a thought gets, the less important it will be.
The worst one can do is to "fight" against a thought. This is where synaptic activity thrives.