Why some say you can lose salvation?

How come some say you can but some say you can't? Verses in the bible
say you are promised the Holy Spirit in John the Gospel Jesus promised
us the Holy Spirit so no, but you have other verses that say you can.

Why is that?

Here is another verse "And I give unto them eternal ife and they shall
never perish"
John 10:28
Why is it the bible says you can but then you can't? Even if you could
lose it what would be the way to do so? I'm afraid maybe I did lose it