Resist the devil and he will flee (James 4:7)
When faced with a temptation or mental obsession, we try to overcome by avoiding it or running away. This is a good defense when the object we are fleeing is greater than we are (think: tornado). We simply cannot face it and win.
Most of the time, however, with our greatest internal enemies-- addictions, obsessive thoughts and fears-- we will at some point be unable to run away. What will we do then? Resist them.
It's like the hiker who was being chased by a mountain lion. As the lion closed in on him, he stopped, turned around and screamed as loud as possible; and the animal fled!
The best defense is a good offense.
Most mental obsessions are rooted in cognitive distortions and lies. The key to resisting them is to confront them with thoughts that are louder than they are, that make more sense, or are more just, right and true.
Most carnal temptations are rooted in craving. The key to resisting them is to supplant them with passions that are stronger, deeper and more meaningful or longer lasting.
Avoidance strategies put space or distance between ourselves and the enemy; resistance actually wins by being bigger, better and stronger.
addendum: I can't help but notice how this is analogous to our fight against COVID-19, and the difference between using masks/social distancing (avoidance) and building immunity (resistance).
