The mind is a canvas. And it takes discernment (and patient practice) to know who is painting on it… us, or the culture or the enemy or God. Not all thoughts we have are from us (and many of our own thoughts are…uh..not that helpful). We cannot afford to be passive as we meander through our brains. We have to be aware and disciplined, and to know the difference between the stuff in our heads and the Word of God:

“…we take captive every thought to make it obedient to Christ.”
(2 Corinthians 10:5)
us, or the culture or the enemy

These 3 could be all the enemy, depends upon who one has chosen to submit to at the moment the thought is coming into our minds. Either our thoughts come from God or from the devil.

These are God type of thoughts.....
Philippians 4:8
Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things.

As you said and I agree we must know, or learn to recognize who our thoughts are coming from (God or evil). And if they are of the enemy take them captive to the obedience of Christ (anointing of the anointed one).

Blessings! Good thoughts