...you're just focusing on the bad.
It’s not unmanageable when we get one unexpected problem, but for some people, bad things seem to come in bunches. The belief that good and bad luck runs in streaks is common. There may be some good reasons why apparent streaks happen. Causation in the real world is complex. The factors that cause one thing to go wrong may have a connection to other things that therefore also go off the rails. In other words, left unchecked, when one things goes bad, related things will go bad too. Sometimes we recognize these connections, but when we don't - that’s when the string of events is perceived as a bad streak.
A domino effect can occur when one thing goes wrong and directs our attention and focus away from unrelated but important matters and those important matters end up suffering as a result. Our emotional response to one bad situation makes us susceptible to more bad situations. We don’t think clearly when we’re upset. We start wondering what else can go wrong which puts us into a vicious cycle that becomes a self-fulfilling prophecy. If we choose to believe in streaks of luck, that compounds the problem.
Those that follow a metaphysical philosophy will tell you that it goes even deeper then that. If you subscribe to the concept that you create your own reality, then when you say you are on an unlucky streak, the universe provides you with additional evidence to support your theory. Even if you don't believe in any of that mumbo-jumbo, a focus on the negative reveals all of the bad things that are happening and the lens of negativity distorts them, making them bigger than they really are while obscuring the good things that might be happening at the same time.
What to do when you’re having one of those days? If you can, call it a day. A good night’s sleep solves many a problem. A new day’s perspective often comes with obvious answers. If you can’t call it a day, at least take a break. A walk outdoors works wonders.
If you’re dealing with an immediate situation, you have to deal with it now. Take a deep breath and reset your thinking. Think like Spock. Recognize your irrational emotional response and analyze the situation logically. Your inner intuition may be heard more clearly.
Then of course there's the valuable perspective shift of 'will this matter in 6 months?' If the answer is 'no', you're probably spending way too much time fretting about the situation. "This too, shall pass."