Your signature. Read again Hebrews 6:4-6 and you will know who it is who falls away. Are people blind?
It is those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, and have tasted the good word of God, and the powers of the world to come.
The Book of John chapter 10. The True Christian's Salvation is eternally secure.
When we cannot work so as to earn Salvation, as we're told by the Saint Apostle Paul in the Book of Romans chapter 3:20 For by works of the law no human being[c] will be justified in his sight, since through the law comes knowledge of sin, we cannot work to lose Salvation. The Book of 1st John chapter 1:9 If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
You might care to study the subject so as to understand better that when the God of all creation tells us those who are in Christ are eternally secure, that His word is bond. While doubt would pertain to those who are further described in the Book of Hebrews chapter 6. Those who are not truly in faith, or are in the immature and stunted state of belief. Thinking God is not a God of His word, or that Christ's death on the cross did not accomplish what God said was accomplished. Therein thinking there is something that weak believer can do so as to be cast out of Salvation.
It is not uncommon for those who have a surface understanding of scripture, reading just enough to think they know enough, to hold faith in their inability to remain saved because they are certain there is something they can do to lose it.
Why they would argue for that I do not know.
When God said Salvation is eternal and irrevocable, that's God's word. He does not lie, nor take back His Heavenly gift.
Study, to show thyself approved that you might rightly divide the truth of God's word. (the Book of 1st Timothy chapter 2)