Aren’t Changing Circumstances Actually the Fastest & Easiest way to Change Our Thoughts?

I have a friend who spent years expressed negative thoughts about her boyfriend and the home they shared. Her thoughts clearly caused her a lot of negative emotion and unhappiness. Then they got married and moved into a different home. I just saw her for the first time since the change in her circumstance and she’s like a different person. I understand it’s not the change in her circumstance but the change in her thinking that is the source of her positive feelings. Nevertheless, she now expresses positive thoughts about her life that are generating positive emotion for her. Based on this, wouldn’t it therefore be a natural inclination, and even an efficient strategy, to put effort and attention into changing the circumstances in our lives?