I pray because God turns mourning into rejoicing.
Everybody knows what it's like to go through rough times. Whether it be from a family member passing away, financial crises, medical health, emotional health, etc. But, after you make it through the storm, you find yourself rejoicing, and praising God for helping you get through it.
After making it through that rough patch, you are also a little bit stronger and realize how much more you can handle because of it. God always has a way of bringing us into another storm, but we all know storms cannot last forever, and once the storm is passed, the sun shines just a little bit brighter.
If God brings us to it, He will be with us every step of the way, and He will always bring us through it. He also knows just how much we can handle, and if we cannot handle it, He definitely will take care of us through it. If we are not strong enough, God will always be.
There may not always be answer as to why God did bring us to a "storm", and there is not always a "silver lining" to a cloud. But, we are always stronger after we do make it through. "It's all in God's plan" I don't think is a very good answer to the question "Why?" There sometimes isn't an answer, so once the storm has passed, we can just rejoice that God help us through, and that we are stronger because of it. And the rougher the storm, the more we can rejoice once we have made it through.
I pray because God turns mourning into rejoicing.