What keeps you motivated?

I think motivation is the wrong force to use to keep you chugging as an entrepreneur. You only need motivation to start, and maybe a few times a year to shake things up and try a different approach. What you really need as an entrepreneur is discipline. You need to discipline yourself to wake up every day and do the tasks at hand. You also need to discipline yourself to budget your time, and ensure you are working on the things that will grow your business and not just do the fun stuff.

I don't go looking for motivation to brush my teeth every night. It's the discipline that makes it happen every day.

There's been a lot of great stuff said already (discipline, scheduling, talking to potential users, hanging out with other founders) , so I'll take a slightly different approach and say "finding reasons to be hopeful".

Lately when I've been feeling frustrated with procrastination and tiredness, I find myself giving up on my project thinking stuff like, "it's a silly idea that no one wants" or "this process sucks why don't I go learn tennis or something normal". I think the root cause to all those thoughts has been an overall loss in hope; I stop believing that designing/coding/marketing/failing/learning is a good use of my time. Here are some things I do to feel hopeful again:

• Listening to founder interviews (indiehackers podcast is solid along with many other podcasts, and some interviews are with founders who are way far along ie thousands in MRR / users, so I try to filter down to founders who just launched prototype and got their first 100 hundred paying users - their stories remind me that it's possible to do this and they're generally optimistic that they can do more, whereas talking to other founders sometimes turns into complain fests!)
• Giving permission to do nothing today (if I'm finding myself struggling at writing a single line of code and I realize I'm distracting myself by refreshing email/reddit, then I just give myself permission to do nothing productive today; this takes the self-guilt off my shoulders, and usually the next day I'm bored of fucking off and my brain realizes that working on project makes me happy)
• Journaling about how my life can change after this project (this feels like daydreaming, but I find writing in notebook to be therapeutic. I think writing about the "next step" after project helps remind me that this is a good use of my time - I write about the tools I'm learning, the people I meet, surprises that I don't see other people talking about - and usually a few pages + cuppa coffee later I feel rejuvenated to get back to working.

The resistance you're feeling @johnbauer528 is natural and needs to be talked about more. If you want to procrastinate with a good book on this subject, I like how "war of art" explains this kind of blocker.

I love my product and want my users would love it too. Some of them love it so much that bought it. That's enough (for now :)
Another very motivating thing is I have a bhag.

I think when users interact spontaneously with me

Seeing the userbase grow every day gives me the drive to continue. Another thing is that people are actually using your product, the positive feedback and recommendations for improvement.

Hanging around people who get things done. Whether online or off, I think it’s helpful to have others that you can look up to. Listening to podcasts on the go helps me - hearing about all the cool things people are working on makes me want to keep doing that too.

Schedule time for it. Make it a significant enough block of time that you can get into the flow. Make it routine and part of your daily/weekly to dos. I've found that my motivation fluctuates, even when it comes to projects that I am really passionate about. It's hard to keep going on motivation alone. If you're really determined to get your project launched then treat it like you're working for someone else and schedule it in and get it done.