Several of the application questions for The Washington Post Award for Excellence in Nonprofit Management center around planning, as a tool for supporting mission. In the applications I've read, I can see a distinct pattern:
Nonprofits who ask themselves "does this further our mission?" -- and then either accept or decline an opportunity accordingly -- go further in effecting change and reaching their goals. They seem to have happier and more dedicated staff and board members, and are more successful overall.
So, as you're considering:
- a funding opportunity
- collaboration with another organization
- a potential new staff member
- expanding a program
Ask yourself "does this further our mission?".
If not, don't do it. It's critical!