Born in the wrong era? No. There is no wrong era.

some chemical reaction are very exothermic. can be very hot or very violent.
like thermite this kind or when u throw caesium in water.

and then some chemicals just don't react. don't even mix.
immiscible liquids. think oil and water.

and then there are the suspensions like....i dunno throwing sand into water?
hah. this kind u leave it to settle it will settle. mix it up abit and it looks like it's mixed, but actually no la. does ribena count as a suspension?
the constituents may be well mixed but no chemical change has occurred?

and then there are the nice happy chemical reactions.
u mix baking soda with vinegar and u get something new.
the final product may not taste so nice, but final product it is and the constituents are not the same anymore. and we can hope that something good has resulted from the whole interaction.

obviously, the relationship between different chemicals will produce different results and one must definitely factor in the conditions of the interactions as well. think catalysts and atmosphere and reaction energy.

and then also consider that under different scenarios, different reactions are desired.

and so at the end of the day, it is about identifying the chemicals, knowing the interactions and producing the results as is required by the relevant scenarios.

straightforward in theory?
yesh.
simple in practice?
no.