OP, you are completely and absolutely wrong. The private keys ARE NOT randomly generated characters. They are actually 256 bit numbers. This means that the total number of possible private keys is 2^256 - 1, which is a ridiculously large amount of possible private keys. Those private keys are converted into the characters that you see through a process known as Base58 Check Encoding (
https://en.bitcoin.it/wiki/Base58Check_encoding). You cannot just throw random characters together to get a private key because it will probably fail the Check part of Base58 Check Encoding. The Check is the first four bytes of a SHA256 checksum of the private key.
Note that most Bitcoins are spendable by addresses, not public keys. Addresses are only 160 bits, and any private key whose public key hashes to the same 160 bit address is able to spend the coins at that address.
So for most coins it's "only" a 160 bit search to find a private key that can spend them. You don't need to find the same private key as the proper owner of the coins, you only need to find one which gives the same address.
Of course, a 160 bit search is still impractical to carry out. But it's a lot easier than a 256 bit search.
Bitcoin (cold address)-> person can coincidentally create an exact same account number (cold address) .