You lean into a problem, especially a long-term or difficult one, by sitting with it, reveling in it, embracing it and breathing it in. The problem becomes part of you, at least until you solve it. You try one approach and then another, and when nothing works, you stick with it and work around it as you build your organization and your life. [I don't mean you just bully the problem, or attack it. I mean that you accept it, live with it, breathe it and whittle it until you've achieved your goal. Once you start looking forward to your interactions with the problem, then you're leaning into it.]