I've seen a few fun articles about people breaking home grown encryption. The question is mostly about how motivated someone might be to find a problem.
Making a secure encryption algorithm requires a lot of presence of mind, and a lot of industry knowledge. If your threat model is incomplete, you lose. If you forgot one tiny thing at one tiny point in the algorithm, you lose.
If you don't have people checking your work, how do you know? If someone is determined to break your encryption, they are capable of spending a lot more time analyzing it than you spent building it. And they only need to find one mistake.
It's definitely better to use the tools that experts have spent lots of time, lots of breadth of knowledge, and lots of depth of knowledge inspecting.
Making a secure encryption algorithm requires a lot of presence of mind, and a lot of industry knowledge. If your threat model is incomplete, you lose. If you forgot one tiny thing at one tiny point in the algorithm, you lose.
If you don't have people checking your work, how do you know? If someone is determined to break your encryption, they are capable of spending a lot more time analyzing it than you spent building it. And they only need to find one mistake.
It's definitely better to use the tools that experts have spent lots of time, lots of breadth of knowledge, and lots of depth of knowledge inspecting.