You absolutely need to celebrate yourself. It’s not about humility; you can do this when no one’s looking. But if you don’t give your brain a reward when you accomplish something, several bad things happen.
First, you start to lose motivation to accomplish things! Your brain seeks that sweet sweet dopamine, and if you condition your brain that you get it when you achieve something, your natural motivation levels will increase. But if you work yourself to the bone and then don’t stop to give yourself an associated reward, your brain associates toil with… nothing. Just toil.
Second, you need to imprint on yourself that you did accomplish something, or your brain thinks you didn’t! You’ll undervalue yourself and your skills, hurting your ability to negotiate with them. I’ve seen so many “hard workers” chronically accept less than they’re worth simply because they don’t think they have that much to offer. All they’ve done is “work hard,” so their brain fixates on that as their only value-add, instead of the actual results of all that effort!
So when you hit those milestones, have a treat! Dance a little! Do whatever it takes to imprint on your subconscious that you achieved a valuable goal. Your brain deserves it, and so do you!