Deadlines, whether real or artificial, are usually beneficial. Setting deadlines keeps you accountable for the work you do. Your writing is your work, and you should take pride in that. Your goal here is to “turn pro,” not to do work as a hobby that comes and goes.* You should set yourself deadlines as if there is a superior who you must please.
There is. Where this expectation comes from is unclear, but it’s there. You know that this is part of what you’re supposed to be doing. Perhaps you don’t end up writing at all later on in life. That’s irrelevant—this is your journey to get wherever you’re supposed to be. Embrace it. Wake up and work hard. Enjoy it. This is your life. This is your reality.
*See Steven Pressfield’s The War of Art and Turning Pro.