The speaker means at the exact moment s/he is speaking.
The speaker is talking about a temporary action around this time in his or her life
I live in Hong Kong
This is a temporary situation.
This is a permanent situation.
I'm living with my sister unitl I find a flat of my own
This is a temporary situation.
This is a permanent situation.
The course finishes at the end of next month.
This is a permanent situaiton
We are talking about the future.
I'm meeting David on Thursday.
This is a future arrangement.
This is a repeated action.
I meet David on Thursday afternoons.
This is a repeated action.
This is a future arrangement
The weather is getting warmer.
This sentence refers to this exact moment.
This is a changing situation.
Jack and Rose fall in love while travelling to America on a luxury liner.
This is a repeated action.
We are describing the plot of a movie.
He often plays mahjong.
I think he shouldn't.
No opinion is given in this statement.
He's always playing mahjong.
I think he shouldn't.
I have no opinion.
I think we should go home.
This refers to the moment of speaking - now.
This is a general truth.
I think we should go home.
The present simple tense is used to refer to the moment of speaking. The verb 'think' is stative and doesn't take the continuous form when referring to an opinion.
The present simple tense is used to refer to an opinion that the speaker holds always.