Yes, it was. An attack only needs to work one way, but an encryption standard must resist all attacks.

There are many examples of would be crypto algorithms that died on the vine because an attack was found. It is often recommended for beginners to study breaking cryptographic algorithms long before they attempt to create them.

It didn't take 25 years to come up with Symmetric Encryption and AES but even though people try extensively to break it for the last 25 years no-one has come even close to anything that is not brute force (which is practically impossible even assuming very generous computing resources). So at least in that case coming up with the encryption seems to be a very solvable problem but breaking it seems close to impossible.