we make a hypothesis based on some time in the future. The Bitcoin account is one trillion. Assumption: 256 numbers or combinations of letters are 2 trillion (it can be calculated by mathematical formulas, here we make a hypothesis) Then: any modification of the letters in the private key, it will be the private key of an account .
It also applies to altcoins. But the number of Bitcoin accounts is the largest. It needs to make changes first.
Where that 2 trillion came from? As far as I know, the number of combinations you'd need to try is 2^256=1.1579209e+77, which is way much more than 2 trillion.
To me your assumption looks like the following. "Let's assume that the Federal Reserve Bank of New York is left without any security personnel, staff members are blind, other customers don't care, and all the vaults can be opened with a pin. Voila! We can rob the bank!"