What does 'only' represent in following sentences?

Only represent in following sentence that there is just one or very few of something, or that there are no others. eg. Dr. Stone, I

I can only dream of becoming someone like Dr. Stone.

I can only do this for so long.

In these two cases, I believe 'only' is indicating that while multiple outcomes are imaginable, not all are possible.

1. Here the outcomes are a) "you can dream about becoming like Dr. Stone", and b) "you can take action to actually become like Dr. Stone". You will never go beyond thinking about the situation, to making it happen. You are limited to option a.

2. In the second case, I believe the sentence could be reordered to read "I can do this only for so long." In this case the two choices are a) a limited time, and b) forever. You can do only a, not b.