You have to trust the people who figured out the math, when they say "this math is secure". Then you have to trust the people who programmed that math, when they say "this code implements this math correctly". And then you have to trust the binary, unless you compiled it yourself, when it says "this binary compiles this code correctly", and finally you have to trust the machines when they say "this computer executes this binary correctly", all the while trusting youself not to have made any mistakes at any step which will quickly cost you everything you put into the system.

If you are an expert mathematician, programmer, electrical engineer, and white hat you might not have to trust anyone else. How many people are all of these though?

> You have to trust the people who figured out the math, when they say "this math is secure".

Not really. I'm convinced the math is secure given the current knowledge, because there's a massive financial incentive to break it. I don't have to trust anyone.

Similarly, I'm convinced my bank is secure, because there's a massive financial incentive to break it. I don't have to trust anyone.

Your hardware and software vendors, and the people who secured your OS and your physical premises.

Don't you need to also trust all of the other nodes on the network to come to consensus?

No, I wouldn't need to trust any other nodes. Each Bitcoin node checks all blocks for validity from scratch.

If majority of the nodes or the miners suddenly conspire to change the rules, my node will simply ignore those blocks as invalid.