Change What You Can
Academics are the nexus of a university. They interact with other academics at all levels, administration, parents, donors, funding agencies, and corporate partners. These interactions can be helpful and productive, or they can be a source of frustration. While the ability to work with (or around) these groups is a valuable skill, that's not what this post is about. This is about realizing that there are some situations that you can't change. Sometimes the only thing that you can change is your response to a situation.
Things happen. A bad review, a grant isn't funded, a conflict with a colleague, an error by a staff member, somebody steals your lunch (again). You have the ability to frame these events as things that happen to you, or simply as things that happen for you to respond to. You can be a helpless victim, or you can be an independent actor that approaches the issue strategically. You don't emotionally attach, you don't judge, you don't deny your feelings. You look at the whole situation as a set of facts that you can act upon. Things happen outside of your control and independent of you. You accept what has happened and go from there.
This is not easy. However it is a skill, which means it can be trained via practice and focus. You can get better at it over time.
Let's take the case of a grant that isn't funded. One approach is to focus on the lack of overall funding in your research area, the increased difficulty in obtaining a fundable score on an NIH application, the amount of work required to get a fundable score now as opposed to the past, your lazy postdoc who went on vacation instead of repeating what would have been a key preliminary experiment… Or you could internalize the rejection, saying things to yourself like "I'm a bad scientist" or "I can't write fundable grants" or "nobody is interested in my work".
Neither of these approaches is very productive or helpful to you as a person. Instead, you can simply accept the fact that 1) you wrote and submitted a grant with the data you had available at the time, 2) that grant was not funded, and 3) you can control the grant you submit, but not what happens to it once it is submitted. You are just a person who submitted something that wasn't funded. So what to do? Assuming you still want funding, you need to change the grant somehow and try again since that is what you can control. You need to look at what you can do, such as talk to the PO about how the review went, respond to criticisms received from the study section, help your students and postdocs prioritize key experiments, work on clarifying your writing, make sure your proposal is both within the scope of what the funder is interested in funding and that its objectives and approach are clearly communicated, look for alternative funding sources, etc. You stay curious about what you can do, execute on things that you think will be helpful, and move on.