Romans (NIV) > The Spirit you received does not make you slaves, so that you live in fear again; rather, the Spirit you received brought about your adoption to sonship. And by him we cry, “Abba, Father.
If we fear failure in accomplishing what God calls us to do, we are not really doubting ourselves, but the Lord and His Word. Yikes. When we're doing His work, it's less of a failure issue, and more of a faith issue. "Now to him who is able to do immeasurably more than all we ask or imagine, according to his power that is at work within us, to him be glory in the church and in Christ Jesus throughout all generations, for ever and ever! Amen" (Ephesians 3:20-21).