Rome wasn't built in a day. I'm sure everyone has heard that quote, but that's not the full quote. The full quote goes "Rome wasn't built in a day, but they were building every day".
The second part emphasizes the value of consistency.
Good things take time, yes, but time is not enough.
They also require consistent work.
It's tempting to believe you can replace consistency with intensity, that you could be at the gym for 6 hours one day, then not workout for 3 weeks and be fine.
Unfortunately, that's not the case, and you would get better results with 3x 40-minute workouts for 3 weeks.
We often fall into the trap of believing that the same rule of consistency > intensity doesn't apply to other areas of life where it's not as obviously true.
Cramming all day the last three days before an exam may have pulled you through a few exams, but it's not a good long term strategy.
Habits
Habits are the cornerstone of changing yourself, and building habits require consistency.
Even if you got the same result from a 6-hour workout as when split up in 30-minute sessions, it would be worse in the long run because the habit would be weaker.
Habits are built through repetition. If you only do something every third week, you're not getting enough repetition to cement the habit.
A good trick to make building a habit easier is to focus on doing it consistently and not worry about intensity.
You will have bad days, and that's ok, skipping days, however, is not.
Allowing yourself to have bad days lowers the barrier to action.
If you need to give 110% every time you go to the gym, then it's going to be harder to get up from the couch on the days you feel like shit.
I count performing the habit as a win, no matter how poorly I did it. Some days you may only do half a workout with half the intensity and that's fine; you're one repetition closer to having a solid habit.
This is the same for studying. If you're aiming to study every other day, even if you only study for 15 minutes some days, those 15 minutes are going to add up over the months and years.
Just like Rome, good things take time. So focus on being consistent with your tasks rather than performing a few intense sessions occasionally. The tortoise always beats the hare.
Not only skills
Consistency doesn't just beat intensity when it comes to improving at a skill like exercising or programming.
It also wins when it comes to things like relationships.
Treating your girlfriend to a two week vacation in the Maldives is nice.
However, it's no match for telling her you love her everyday or greeting her with a smile and a hug when she comes home.
As far as I have been able to tell, consistency beats intensity in every area of life.