Calvinists believe in the doctrine of the Perseverance of the Saints, which holds that those whom God has called can never fall away. Because God chose some to be saved, he keeps them from apostasy and those who do apostatize were never truly born again.
Some non-Calvinists advocate a similar doctrine of Eternal Security (“once saved, always saved”) teaching that once a person is saved, his or her salvation can never be lost.
Arminians generally believe that salvation is secure and protected from all external forces, but it is conditional on us remaining in Christ, and it can be lost through apostasy. Salvation is conditioned on faith, therefore perseverance is also conditional. Apostasy (turning from Christ) can be committed through a deliberate, wilful rejection of Jesus and renouncement of previous faith.