I imagine that once upon a time a mountain lion casually strolled into some ancient family's hut on a cold winter night and settled down in front of their fire and the entire family was too terrified to shoo it out. After spending the night enjoying the warmth, it probably left on its own and then came back the next night to keep warm, basking happily in front of the flames while the poor family spent yet another sleepless night huddled in fear in a corner, waiting to be mauled to death but too afraid to attack the cat. Eventually someone probably gave it some food and then maybe a child got brave and gave it some ear scritches and it realized that why should it go live a harsh life in the wilderness when it can rule the home and be treated like a god? It then went out and brought back the rest of its family or tribe and that's how cats became "domesticated"