This and that when they refer to non-tangible objects

Let’s take this example:

….But on a regular, day-to-day basis, when a task requires thinking
that isn’t itself enjoyable, even puzzle lovers’ brains prefer less
thinking over more.
That is the law of least mental effort.

This, of course, has major implications for our decision making,

• Why in the 1st case it’s "that", and in the 2nd "this"?
• What would happend if it was the opposite – this, then that – instead?
• What if there were 2 "this", or 2 "that" instead? How would the meaning have changed?