It's OK to be sad if you didn't receive the job offer you wanted, but try to remember this is all new for everyone — and nobody knows what to expect. Perhaps there were budget cuts or lay-offs that prevented the company from continuing on with the interview process. Instead of ghosting the hiring manager after receiving your rejection letter, send a thank you email and say that you'd like to stay in touch. Who knows, the hiring manager may reach out with a new opportunity in a few months, or perhaps the recruiter who emailed you way back when can connect you with the hiring manager of your dream job!