Computers are only capable of making pseudo random numbers, since they must calculate random numbers in certain ways to generate them.
If you use password manager apps on your phone or desktop, using human-picked, computer-generated master password might be actually a big security threat!
Diceware is one way of making very safe password.
Diceware is easy to remember, very hard to break.
This app generates Diceware passphrase using Quantum Random Numbers, which is powered by ANU Quantum Random Numbers Server which generates true random numbers by measuring the quantum fluctuations of the vacuum.
If youd like to read more about the quantum random numbers, visit http://qrng.anu.edu.au/