Jesus says in John 10:27-29 (KJV): My sheep hear my voice, and I know them, and they follow me: And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
Many false Christians say that nobody can take Christians out of Jesus's hand but Christians can get out of Jesus's hand themselves if, for example, they commit too many sins. But this is false. "Neither shall any man" means no one. No man and no woman. Are you any man (or woman) ? Yes. But the Bible also says "they shall never perish", meaning that they will never die spiritually. They shall never perish. Never.
So, if God the Father gives you to Jesus, you shall never perish. If Christians could lose their salvation by plucking themselves out of Jesus's hand, it would mean that the part where Jesus says "never" is false. "Christians" who say you can get out of his hand are indirectly saying Jesus lied when he said "never". They call Jesus a liar.
The apostle John says in John 3:36 (KJV): He that believeth on the Son hath (present tense) everlasting life. And Jesus says in John 6:47 (KJV): Verily, verily, I say unto you, He that believeth on me hath (has) everlasting life. You receive the gift (Romans 6:23) of eternal life the moment you truly put your faith in Jesus.
Once you have this gift you are in Jesus's hand and you will never perish. Never perish means that no one, not even yourself, can pluck you out of his hand. If you think you could pluck yourself out you're thinking Jesus lied.