"Think" vs "Thinking | "I think" or "I'm thinking" (present continuous)

When think means 'believe' or 'have an opinion', we do not use the continuous:

- I think Harry is Mexican, but I'm not sure. (not I'm thinking)

- What do you think of my plan? (What is your opinion?)

When think means 'consider', the continuous is possible:

- I'm thinking about what happened. I often think about it.

- Thomas is thinking of giving up his job. (=he is considering it)