To send in your manuscript to publisher after publisher is - to say the least - a daunting situation. The worst is that you often won't find out why your book was declined and it leaves you guessing. For a lot of us, it can also make us start doubting not only our manuscript but our capability as writers. This is why we need to keep our head cool through this process and keep sending our manuscript to the publishers.
Don't give up! Remember, it is only those who keep trying who will eventually be a published author. No matter the excuses.
But what can you do to keep going? What motivates me? I get a lot of declines but I need to keep sending my material in and this is what I do to motivate myself:
1. As soon as I've finished a manuscript I start writing on my next one. I don't stop, I keep going.
2. I have a few post-it-notes in front of my desk which motivates me. They read: A: "You can have everything you want when you're patient".
B: "The trick to being published is about sending your writing to the right place".
C: "What received a no was that specific manuscript submitted to that specific publisher, because it wasn't right for them at that specific time. I'm still a great writer and there is another publisher who's going to want my book".
Keep following your dreams!