Diagonal argument proves that real numbers are bigger than natural numbers. Let's say you made a list of natural numbers till infinite and put them in one to one correspondence with different decimal numbers.
1 → 0.154967906.....
2 → 0.646907689.....
3 → 0.896865555.....
4 → 0.467877998.....
5 → 0.987789556.....
\
\
(till infinite)
Now we think we have listed all of decimal numbers that can exist in correspondence to all natural numbers that can exist, no one is left since both are equal, infinite, yeah?
Now take one values from all the decimals we have wrote (and would have wrote till infinite) from alternate places (not same, you're not supposed to take values from 10st decimal place again from another decimal number if you have already taken it once). You'll get smth like: 0.14688....
Now switch the all of decimal places of number we have created from any other number, 0.14688.. will become 0.26499..., now 0.26499... doesn't exist in the list we created previously, it doesn't exist for "1" since it doesn't have "1" at 10th decimal place, it doesn't exist for "2" since we doesn't have "4" at 100th decimal place, etc.
So we got extra number that can't be listed in one to one correspondence with natural numbers, now you can just list it inside the list again with the list by adding 1 more number in the list of natural numbers and it's size won't increase since "1 + infinite = infinite" and repeat the same whole process we did above and you will get again one more decimal that doesn't exist in the list then again and again and again... adinfinitum. You'll always get one decimal number left regardless how many times you do it. That shows it cannot be listed in one to one correspondence at all since they're not equal, clearly, set of decimal numbers are bigger than set of natural numbers, so large that infinite+infinite+... won't reach it. That's uncountable, decimal numbers are uncountable. Now it's time for me to run away since, no more. Gtg nice to cya and have a nice day.