Instead, recognize it for what it is—a sign that important evidence has been building up in your buffer, unacknowledged, and that it’s time now to integrate it into your plans.

Maybe. On the other hand, I also recently read another article on this, which attributed things more to emotional oversensitivity to a lack of progress, which might also be a reasonable explanation:

A while back I wrote about how the nonlinear life and our linear emotions aren’t exactly optimally suited to each other. Your brain craves signs of progress, so it could reward you with a burst of feel-good chemicals. Unfortunately, the nonlinear life doesn’t work like that. Often, you can spend days or weeks slaving away at the office/studio/whatever, not really moving forward – or even taking two steps back for each move forward. Despite the hours that you put in, the article/thesis/design never seems to be finished, making you question whether you’re really cut out for this kind of job. Perhaps you’d do the world a favor by setting your sights lower and working as a sales clerk instead. [...]

...let’s assume that we have a project that has a goal we’re trying to reach. Arbitrarily, let’s say that the completion means we reach a threshold of 100 points. Of course, these numbers are completely make-believe and I pulled them from my magical hat. Now, further, let’s assume that each unit of time – say 1 unit equals 1 day – means we have three possibilities: make progress, stay where we are, or take steps backward. In my personal experience, this is an ok model for work: sometimes you’re actually making progress, and things move smoothly. Sometimes, though, you’re actually hurting your project, for example by programming bugs into the software, which need to be fixed later on (just happened to me two weeks ago). Most often, though, you’re trying your best, but nothing seems to work. Maybe you’re stuck in a dead end with your idea, and need to change tack. Maybe you’re burdened with silly tasks that have nothing to do with the project. Well, I’m sure we all have these kinds of days. So let’s again use my magical hat and pull out some probabilities for these options. Let’s say you have a 5% chance of making a great jump forwards (10 points), 25% chance of making 3 points of progress, 55% chance of getting stuck (0 points), 10% chance of making a mistake (-2 points), and a 5% chance of doing serious damage (-6 points). Now we just simulate these across and get a graph that shows your cumulative progress towards the goal (yes I'm doing this in Excel):

Even though the numbers are really made up, I feel the above graph is actually a pretty decent example of how the nonlinear work often feels. However, there’s still the additional complication: the emotions.

Suppose that our emotions work as follows. If you’re making progress, you feel good. And this is mostly irrespective of how much progress you’re making. Suppose the same holds for drawbacks – it hurts, but it hurts almost as much to look for a bug for two hours or the full day. Finally, I’ll assume that if you’re not moving anywhere, you inherit the feeling from the day before. [...] So with these assumptions, we get the following graph portraying emotions:

[...] I think the above graph is quite a good summary of how the nonlinear life often feels: you love you’re job, but you’re not above hating it when things are not going well.

Which isn't to say that "don't resist the slide down to despair, instead take it as an opportunity to evaluate the information" wouldn't be a good idea (indeed, that's a reaction that I'd recommend each time one feels a negative emotion), but on the other hand, "are my emotions just ill-calibrated for nonlinear progress" might be a good question to start the evaluation process with.