Some of them think: "I'll never learn enough to be a good developer." Probably you are thinking the same too I have bad and good news about it, but the good news outweigh the bad news, thankfully.
Think of programming languages as tools in your tool belt. The more tools you have, the more things you can do. But you already can do many things with the tools you already have.
And one of the keys to improve as a developer (and any skill) is just being persistent. If you keep learning and practising, you'll become a better programmer over time.