It is not like you believe - that your beliefs are all your own. I mean, like, who really has the time to learn everything about everything. So, most of what you think you know are things that you have picked up from what those around you state that they know. AND...well, it is not as though THEY have the time to learn everything about everything. And so...
Tiru has this to say about it.
Nilatthiyalbaal neer thirindratthagum maandharkku inaththiyalba dhaagum arivu - Tirukkural
Just as water takes on the qualities of the land it flows through, people take on the knowledge/attitudes/beliefs of their associates - Loose Translation
You can see that clearly demonstrated in the world at large. Like, take education for example. You'll find that some people seem to overrate it and some underrate it. AND it will be a community thing. Like, in the US, Indians (and Chinese?) push their children to heights in education but not the native westerners. The community values education and, as people who like being respected in their society, the members of the community follow suit. Attitudes being driven by the community.
Beliefs are the most common thing that society pushes on you. Religion, for example. THAT's driven into you from birth. So strongly that, later in life, some are willing even to take the lives of followers of other 'false' religions. Despite the fact that the belief did not start out as their own choice. You are born in a certain family, belonging to a certain community and, presto. Take beliefs about whole other communities - as cunning, cruel, whatever - with no personal experience of the same. Are they yours completely by your choice?
The strange thing is that knowledge itself is dependent on associates. I mean, it is not like you support the Pythagoras theorem or oppose it based on who you associate with. When it comes to things like 'Did the Mughals oppress the Hindus?' OR 'Does the US deep state influence Indian elections?' or some such, what are the 'facts' that you know? Yeah, right! Most of what you know is what is being discussed among your associates, none of whom has the time and energy to learn history or analyse geopolitics or whatever is needed for an understanding of that question. And, thus, most of those opinions are likely to be ill-informed opinions. Not to mention the fact that the selection and interpretation of facts is also subject to bias.
Or, in other words, over a period you and your associates end up creating an echo chamber of your own. Now, echo chambers may have existed from the times of Tiru but it is only now, in the times of Social Media, that the echo chambers have been fully proofed against external influences - including facts and concepts - that may interfere with the echoes that you so love in that chamber. Perfection, at last!