I fear for my financial future - will I have enough? Consequently, I act in a stingy or dishonest fashion in the present, or perhaps I just live in a way that is sinfully conservative, venturing and risking nothing financially in order to secure my future. Fear leads to sin.
I fear for my acceptance with God - am I good enough? Consequently, I seek to build my own righteousness, work hard at being the best I can be, or perhaps I just steer clear of any contact with the world that might dirty me, and in so doing pass up the opportunity to be a witness. Fear leads to sin.
I fear for my relational abilities - can I really sustain a marriage? Consequently, I am tempted to retreat into fantasy and avoid reality, or perhaps I just fail to open up as much as I should. Fear leads to sin.
The most absurd fear I am aware of in myself (the foregoing are not necessarily autobiographical, but this is): I fear that the gospel doesn't have the power to stop me sinning, so I decline to deploy it when I am tempted, just in case I see it fail. Fear prevents me from fighting sin!
No wonder one recurrent message of Scripture is: Do not fear!