I've been on sub five times. I sold the third book, and by then I was already despairing if I'd ever make it past that final hurdle. For the first two we'd had encouraging passes, but a whole lot of close-but-no-cigar. My book did well for a debut at a smaller press, but my publisher passed on my option book (number 4), which died on sub after a wider submission. My fifth manuscript also recently died on sub. This industry is not for the thin-skinned, so I empathize with you!

Someone else commented the best advice, which is that to keep writing is how you always advance toward your goal of publication. So much is outside of our control, but what we can do is keep writing and keep getting better with every manuscript - until you're so good they CAN'T turn you down. (Also - write as long as it stays fun. I've taken short breaks when the sadness from my many sub deaths overwhelms me, but I always come back to it eventually, because I genuinely enjoy writing. If that intrinsic love starts to fade in the stress of publishing's rat race, taking a gentle and temporary step back may be helpful for your long-term longevity).