No. You learn to do cryptography. You get a book, you sit down and you read it. Understand what are cryptography primitives. Understand how they can be used together to create cryptographic systems. Understand every part of that system. Then learn what are the common errors, learn how misuse of cryptographic primitives can lead to disaster. Be able to talk for hours about why WEP encryption can be easily cracked by a low-powered netbook.

When you've done all of that, you'll know that you are abysmally incompetent at cryptography. When you know that, you can start learning how to become good at cryptography. Some people divide learning in four steps: unconscious incompetence (you don't know that you're bad), conscious incompetence, conscious competence and unconscious competence.

Even when you're competent, you will make mistakes, because cryptography is very hard. We've seen how MD5 is now broken, yet still people use it as message authentication ciphers even when it's trivial to perform a length extension attack. But MD5 wasn't always broken. I'm sure it was designed by competent people, but they can't foresee all flaws.

That is why someone who is incompetent at cryptography should not do it.

(I'm very much not any kind of expert on Crypto but...)

Probably when you understand "Applied Cryptography", front to back, maths included, then you can think about writing cryptographic software.

Or win a fist fight with Schneier.