Premature optimization and Premature pessimization related to C++ coding standards

Herb Sutter's C++ coding standards says to avoid Premature optimization and Premature pessimization. But I feel both is doing the same thing. So expecting some help to clarify these two concept with the difference between them. If you come-up with some examples, It will be more benefit for others. Here is a good explanation about Premature optimization. But I couldn't find any for Premature pessimization