Taking about twice as long as I could have at the university while it was obvious the entire time that I wasn't putting the necessary work into learning the heavy math I would need if I wanted to be a successful grad student. Should've failed fast with the research career aspirations and graduated as fast as I can. (You pick your own course load and usually work up to a Master's degree in Finnish university. There are grades, but generally only graduate studies programs care about them, so if you know you'll go to industry, you can load up on the courses and treat any passing grade as good enough.)