The Present Simple is the most commonly used tense, and this is quite appropriate considering its Core Characteristic. It is mainly used to speak about things we do every day, or things that we know will happen on a regular basis. In this sense, its Core Characteristic is best understood as expressing Fact or Routine. This routine can be related to the natural world, like in the statements, The sun rises in the East, or Water boils at 100 degrees. These statements will always be true, which is why our Reference Point (R) covers all points in time:
In Diagram 1, we have placed Reference Points (R) in the Past, Present, and Future, because those statements deal with regular actions that are universally true. When we want to talk about specific points in time for regular actions, Present Simple can stretch or expand our Reference Point (R), depending on what information we add (see Diagram 2). So, Present Simple is great for talking about someone's routine, such as:
My friend swims every weekend.
I leave my house at 6am every morning.
In Diagram 2, we have placed the Reference Point (R) to show that this routine is part of the speaker's lifestyle. It has been happening for an extended period in the past and is expected to continue into the future.