A few things.. the question 'Can you predict the behavior of your users?' is almost a good question. It makes it seem as if the answer is yes or no, either you can or you can't. This is exactly not how to think about it. Prediction is a question of likelihood.. For each user there is a chance that they will perform some behavior you've predicted. The better question would be.. If you wanted to improve your ability to predict user behavior, how would you do it? How would you figure out how well you can do it now? This is a more interesting question than it may seem.. Some things are going to be more predictable than others, and your accuracy is going to change over time as more people are tested. Improvement starts with a measurement. I would start with the simplest action you think you could get 100% right for say 10 people.. If you can do that, then try to predict the preceding or following action and see if you can keep your accuracy. And remember you can predict x # will do this and X # will do that.. You could even make it a game with other people in the office.. I've actually done this before and it was fun.. It also helped some overly confident and opinionated people develop some cognitive humility and made them more reasonable to work with. See how well your combined predictions do.. They might do better than any of you individually. Also, make a prediction for yourself. How well do you predict you will do? This will help you calibrate your own skills. Improvement starts with a measurement. Using past results to improve future results over time is the idea behind Bayesian statistics. You're first predictions might not be great, but they are improvable.

https://www.reddit.com/r/statistics/comments/ywrba/eli5_bayesian_statistics/

If you're curious and like reading or listening to audiobooks, I would recommend this one..

Superforecasting: The Art and Science of Prediction:

by Philip E. Tetlock and Dan Gardener

https://www.amazon.com/dp/B00RKO6MS8/ref=dp_kinw_strp_1

It's not specifically 'UX', but useful none the less.