We all know that firefighter/fire officer/chief that is always complaining. It doesn't matter, they always have a complaint.
Is that the type of person you want to be around? Are you that person? Who wants to be around be around the person that always has a complaint?
I suggest that it is better to find the good in a situation. I once had an Assistant Chief that always had a complaint about our training exercises. He never could find a positive word to let us know that not everything went wrong. I'm certainly not saying that there weren't areas for improvement, but the entire operation wasn't a disaster as was often his sentiment. I remember when we would debrief the training, I would always say something like "we all had our protective clothing on correctly." Do you know, that would actually make him more disgusted!
When all else fails, look for the opportunity to be positive.