When I comment on atheism I routinely comment on people who are very self-conscious about their godlessness. Their atheism defines their core identity. Their personal and social identity is conditioned by their commitment to atheism. They organize their thinking, speaking, and acting around atheism as a central reference point. They think about God as much as Christians do.
By contrast, there's another kind of atheist. They barely think about God at all. For them, God is not a frame of reference one way or another. They live without taking thought of God. "Alienated from the life of God" (Eph 4:18). They resemble pre-Christian unbelievers who were born before the missionaries arrived.
It's like a concentrate camp which has a door with an illuminated exit sign. You can see it day and night. The inmates walk past the door every day. Many times a day. Back and forth.
Yet no one tries to open the door. No one puts his hand on the doorknob to see if it turns. They don't register the door. It's as if the door isn't there.
They could leave the concentration camp at anytime. But they remain in the camp year after year, decade upon decade, until they die of old age. Freedom lies just beyond the door, but they die in captivity, for their captivity is psychological rather than physical. A prison of the mind.