Christiano,2017, abstract stated that
Macroeconomic policy questions involve trade-offs between competing forces in the economy. The problem is how to assess the strength of those forces for the particular policy question at hand. One strategy is to perform experiments on actual economies. Unfortunately, this strategy is not available to social scientists. The only place that we can do experiments is in dynamic stochastic general equilibrium (DSGE) models
I am quite new to this model, so I have some questions as below:

1> What does "competing forces in the economy" mean? I googled but there is no result so far

2> Why we can do experiments is in dynamic stochastic general equilibrium (DSGE) models ?

I did a search about DSGE model but I did not fully intuitively understand it from this description.