Deep work
When you have a clear problem area and you set aside distraction-free time to work on it.
Used in combination with strict time blocking, this approach can really foster productivity.
Carl Jung built a whole separate house on the outskirts of Zürich, mainly as a deep work-refuge. This is where he generated much of the work that challenged Freud and his contemporaries.
Anecdote. One (profilic) professor, split his year into two: one semester he was very available to his students, he gave lectures and the door to his office was always open. The other half, his door was locked and he was totally unavailable while doing deep, unobstructed work. This actually created a sense that the professor was very available to the students, and it was very clear when he was not. See Structured availablity. – Cal Newport Deep Work on YouTube
References
Cal Newport on YouTube
To follow up
Lex Fridman in a 3 hour conversation with Cal Newport (YouTube) on the topic of deep work, time blocking etc.