Opening the book…
The hard job is where you find out what you are actually made of, and it is also where standing back does the most visible damage to the people around you. Taking it before you are asked removes the politics from the decision — nobody had to persuade you, and nobody else had to lose. It is competitiveness aimed at difficulty rather than at colleagues.
When the room goes quiet over the ugliest piece of work, speak first. Take it without narrating your sacrifice or collecting credit for the volunteering itself. If you are genuinely not the right person, say who is and offer to help them carry it.
Don't take the hard job when someone else needs it to grow — hoarding difficulty is its own kind of ego. And if you are already at capacity, volunteering is not courage, it's a way of failing two things at once.