Multiple sessions

When I mentioned earlier how you should limit your deep work sessions to around 2 hours, I don't mean that you can understand any topic in that period of time. Some complex topics may take days, weeks, months, or years to properly understand. So, it is completely fine to spend a number of sessions working through the same concept. If you are going to do this, I recommend that you make notes for what you were doing when you stopped. This will allow you to pick up right where you left off.