I don't really think that things happen for a reason. I don't even think it's helpful for me to think that way, because to me, then I'm always waiting (good or bad) for the other shoe to drop.
For me, I just try to live in the moment. I have a job (construction management) where "things happen" ALL the time. No matter how well we plan in advance, there are always unforeseen circumstances that come up, and it is only normal to feel disappointed when things don't go as planned. Rather than dwelling on it, I try very hard to just move forward, develop a plan B, and get going on it. Some days that's easier than others. Some days I come home and decide to have a glass of wine, or a bubble bath, or read a mindless book to try and unwind and take my mind off of it. I try to remember that I have no control over other people's actions, only over my own reaction to them.
As a side note, I've noticed that it's often times a lot harder to let it go when I'm under a lot of stress. A few weeks ago at work I was under a ton of stress, and I found myself waking up in the middle of the night, unable to go back to sleep because I was re-playing events in my mind. As much as I tried to let all of the negativity go, it was clearly preying on my mind and was more than I could handle. As such, I had to take a step back, ask for additional help at work so I could re-adjust my workload and become effective at my job again - sometimes when you are having a really hard time at work, you need to evaluate why that is. Have you bitten off more than you can chew? If so, what can you do about it? How can you regain your work-life balance? If you are working 24/7 in order to bring in more income, are there ways you can reduce your need for this income through other areas of your life? Is this short-term, and you just need to get through a certain period of time? Do you need to hire help in order to run your business and still maintain your sanity? Just some things to mull over. Things will always happen in life, as you know, but if you find you're unable to roll with the punches, it may be time to make some changes.