Any area that we are not Overcoming sin is an area that we leave open as a "Foothold" so to speak...
People who struggle with porn won't typically speak out against Sexual mischief....
People who struggle with gossip, scandal, and hating others won't speak out against the same....
People who struggle with cowardice and fear of speaking The Word won't speak against the same...
Etc..
Another is not wanting to "Hurt the feelings" of the secular world - or even fellow believers... One of the ways that we prevent ourselves from being Calloused, Hardened, and Jaded against the pain and guilt of sin is to tell ourselves that it's OK... To give ourselves an excuse that it's OK to practice whatever we want... We use the excuse of "I am forgiven" .. "We have grace"... Etc... Eventually - we push through and callous over the pain/guilt spots in our conscience.... Notice that this action on our part actually PREVENTS us from overcoming and from fighting - as we simply accept our condition as "Ok"...
But remember - we still have God's "Hedge" around us to some extent protecting us.... So - while Satan may have a foothold to torment us and hamstring our ministry to render us ineffective through the ongoing sin - he does not have the authority to attempt to make us Curse God.....
As such - we must remember that it's not our OWN faithfulness that keeps Satan at bay - but rather God's faithfulness and love for us... It's not US who have the power within us to keep Satan out of our lives - it's God...
When we look at Job Ch. 1 and 2 - we see the effects of the "Hedge" being removed.... Most of us have no idea what it's really like when that hedge is removed.... Literally - your whole world crashes down around you and everything you touch falls apart... Even your husband/wife may turn against you (As Job's did).. Your church is against you - everyone and everything in your life turns completely upside down... We have no personal power to stop this - it's all within God's control... Frequently - these times end up being periods of intense spiritual growth - and in hindsight, we see this... but we often don't see it while going through it...
Thanks