The Bible does not promise that all true believers will live victorious, holy lives.3 Believers may have more than temporary setbacks and bouts with sin. It is sadly possible for believers to backslide terribly and to remain in that backslidden state until death. I'm not saying that eternal security is not true. As already shown above, it is. What I am saying is that there is no guarantee in Scripture that eternally secure people will live overcoming, victorious lives here and now.
Believers can fail.
There is a variation of the view just discussed which recognizes the possibility of failure in the Christian life. All believers are overcomers the moment they believe. While I am unaware of anyone who has put this view in writing, I know a number of people who hold it. I myself held this view for several years. It wasn't until I studied the seven letters of Revelation 2-3 during my doctoral work that I concluded that this wasn't what the Lord had in mind by the use of the word overcomer in Revelation.