Most, if not all, economic variables depict a convergent system. This means that no economic variable can’t go unlimited up or down for ever.
A loose fiscal policy is intended to rise GDP by directly investing or spending public resources. It’s great!
What forces prevent this strategy from being constantly or unlimitedly applied? (1) The rise of real interest rates, (2) crowding out effect, (3) expected long-term efficiency of public spending/investing, etc
So, loose fiscal policies will be a one-shot strategy and are expected to be counter-cyclical. A government with a loose fiscal policy for an extended period of time will see its country perish. Example: Venezuela.
If I understand your question, you are concerned about how a rise in interest rates will provide future economic growth. As I said first, the system is dynamic but must remain convergent…
Assuming we are in the depressed market:
One option is a loose fiscal policy > GDP grows > Real interest rates go up > Loose fiscal policy again? Bad idea, stay away > Higher rates compared to international rates attract capital from abroad > Domestic savings increase > Real interest rates may go down > Higher investments and spending > GDP grows > Loose fiscal policy again? Bad idea, GTFO…(and so on)
This dynamic system is convergent. It means variable fluctuate and affect the other variables in order to maintain order. Nonetheless, the system can be shocked by external (exogenous) variables like political events, natural disasters, generalized craziness of million of grannies, etc. and require a new strategy (fiscal or monetary) to bring it back to is long-term (potential) growth path.
The same analysis can be done for a tight fiscal policy, loose or tight monetary policy or a combination of both. Central banks around the world (assumed to be independent from governments) use complex econometrical models to assess and quantify the impacts of this kind of macro decisions. It is quite interesting.