What version says you will never fail? Most versions state fall or stumble, which means SIN.
You don't like fail?
Stumble is the same.
To trip, to fall.
It COULD mean sin, but check out the very next verse which would make it seem more serious than one sin:
2 Peter 1:5 11
"for in this way the entrance into the eternal Kingdom of our Lord and Savior Jesus Christ will be ABUNDANTLY SUPPLIED to you."
NASB
IOW, If you do not stumble, or fall, or fail, the entrance to the Kingdom WILL be available to you.
verse 12 tell us that we are TO PRACTICE the truths that Peter is giving us.
verses 5 and 6 tell us how diligent we are to be.
WHY ALL THESE WARNINGS IF WE'RE SAVED NO MATTER WHAT?
If eternal security were true, WHY would all these Writers give us so many warnings??