Bitcoin’s security is unparalleled for a protocol that stores value. The explanation as to why that is, is very technical and not necessary for the average user to understand why they should sleep soundly while they hold bitcoin.
The best and simplest argument in favour of the security of bitcoin is simply that the wallets thought to be owned by Satoshi Nakamoto add up to about 1.1 million bitcoins (Source https://bitslog.com/2013/04/17/the-well-deserved-fortune-of-satoshi-nakamoto/ ). In today’s rates, that is about 49 billion USD. It’s like a bounty, just sitting there, teasing every single hacker, thief, cryptographer on the planet. It’s there for the taking, if you can break bitcoin’s security.
13 years in and so far nobody has managed that.
Also here’s the livestream where I made this picture.