This is a key feature that makes One-Time-Pads (OTP) perfectly secure. You can't "crack" a OTP encrypted message because depending on the pad you can produce an

This is a key feature that makes One-Time-Pads (OTP) perfectly secure. You can't "crack" a OTP encrypted message because depending on the pad you can produce any possible string, so you can't possibly know which is the "correct" pad. With something like AES-CBC very few output streams are actually possible. So if you guess a key that produces an intelligible message it is very likely correct and even if you brute-force the entire keyspace there is a good chance that only one key produces a plausible result.