The status of slavery and whether a slave remained a slave for life varied widely based on the time period, culture, and legal framework in question. In many historical contexts, particularly in ancient Rome and the antebellum United States, slavery was indeed often a lifelong condition. Slaves could inherit their status from their parents, and there were typically no legal avenues for them to gain freedom.
However, in other cultures and times, slaves could be freed under certain conditions, such as through purchase, manumission (the act of a slave owner freeing their slaves), or after a certain period of service. In ancient societies like Greece, some slaves worked towards their freedom through contracts, and in various African societies, slavery could be more flexible.
Overall, while many slaves in particular historical contexts remained slaves for life, this was not universally true across all cultures and time periods.