There's an area of Rust that you may be the only expert on, or one of only a few experts on. You're spending much of your time dealing with issues in that area.
Just right: You give feedback to colleagues, fellow team members, and potentially the broader community, that Rust needs more experts in this area. You prioritize work that allows new or intermediate users to ramp up into your area of expertise. You spend time mentoring others, producing documentation, and similar, sometimes (not always) at the expense of doing the work yourself. You sometimes turn down action items that only you could do, and instead discuss what would need to happen so that that action item doesn't need to get done as urgently.
Too much: You push back on other changes and obstruct other work on Rust. You try to suggest that further work in a broader area shouldn't happen because you're too overloaded. You propose to give up on the whole area because you don't have time for it. You consider the merits of taking up alpaca farming instead of teaching sand to think.
Too little: You lean into your position as the sole expert in the area. You start to brush off new users, other interesting projects, or other aspects of the community, because you don't have the time or bandwidth. You have less fun working on Rust than you used to.