Accountability means having a sense of responsibility to finish a task or project assigned to you. However, it is more difficult to be accountable of something if no one is keeping tabs on your progress. That is why it is a good idea to have a buddy or colleague to keep you in check.
The Bible teaches holding each other accountable on several occasions, particularly when it comes to spreading the gospel and serving the Lord. Everyone of us are given 24 hours a day to live our lives pleasing to the Lord, and we can work together to make sure that we stay on the course.
Obviously, holding other people accountable for their actions also means giving necessary corrections for their improvement. The same way, they are also responsible to give you constructive criticism about your work.