@garce, if I understand correctly, you have some projects that you are accountable for the outcome to a boss/supervisor. In the corporate world, I'd imagine that these are part of your work plan that you and your supervisor have agreed upon, or projects that you yourself have undertaken to meet your own personal goals. Failure is generally not an option. On the other hand, you're good at what you do, so your coworkers ask you for input on their own projects, but these don't directly align with your predefined work.
I think
@TesTeq's advice (as I understand it) is insightful: each of these types of projects represents a commitment you've made to yourself. By accepting the request, you are holding yourself accountable for some portion of the outcome. You "truly own" all of your projects, and each requires its own level of planning, monitoring, and pushing toward a desired outcome.
In my own corporate (and non-corporate) experience, if I found that when my project list is unclear or overwhelming, I review my higher horizons. This often provides the clarity and confidence to abandon or politely reject some projects, defer others, and focus on the highest impact work. An open line of communication with my supervisor has been key in helping me prioritize my projects on a strategic level.