Some argued with me that my #Bitcoin is nothing else but some numbers in a computer, how can I think that is sound money ?

I mostly replied:

Check what the numbers you see in your bank account are.
Check what the difference is with "my" numbers.

None came back to me.
And since they are still not turned Bitcoiners, I know they still don't realize both are 'just' numbers on a computer.

One are numbers controlled by banks/goverment, can be created out of nowhere and the bank states black in white it is not your money if they "store" it for you. If you want to use your numbers you have to ask them permission, want some of it in person they ask what you are gonne do with it.

The other are numbers controlled by a protocol.
No one controls those numbers, the 'release' of new coins is fixed in a scheme, and is ever slowing down untill a maximum of almost 21 million Bitcoin is realized.

I don't pay anyone to store my numbers.
No one can prevent me from interacting with the protocol.
No one can freeze my numbers or confiscate my numbers.
No one asks what I do with my numbers when I transfer them.
Even if goverment declares me a terrorist nothing changes to above.

The one 'down side' is that no one else is responsible for those numbers but me, and I like it that way !