Since I was young, I have always found a particular phenomenon when I tried to achieve a goal: If I try over and over again and continue to fail, then when I finally give up and try one more time just to go through the motions, that is when I succeed.
I think it relates to the story about water: if you clench your fist to hold it tightly, you end up holding nothing. If you keep going solely on your resolve, there is no reason to expect the outcome to change. Eventually, you need to do something different And that may mean giving up.
Fortitude is important, as is one's resolve. When you are sending out your writing to publisher after publisher, it is out of your hands. You just have to keep doing it until you've tried them all. But, once you have sent it out to everyone you know, give up.
It may just be a remarkable coincidence unique to me, but I find that hard to believe. I think sometimes we just get tunnel vision and lose focus on the big picture. If nothing else, try giving up just to know that you've tried it. You may find out that you finally got everything you wanted just by not wanting it anymore.
Life can be a serious dick like that.