What if someone guesses my private key?!

A pretty reasonable concern from new Bitcoin users. Let me get you a better insight with numbers.

There are exactly 115,792,089,237,316,195,423,570,985,008,687,907,852,837,564,279,074,904,382,605,163,141,518,161,494,336 possible private and public keys.

To put that into perspective there are roughly 10⁸² atoms in the observable universe. That are 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 atoms.

You can even try your luck finding private keys to a wallet that has Bitcoin via https://keys.lol but you’ll pretty quickly come to the realization that it is more likely to win the lottery five times in a row.