it was believed subjective marginal utility describes barter but not monetary transactions prior to Mises, then he observed:

the purchasing power of money today is based on its expected purchasing tomorrow
purchasing power yesterday traces back to barter; "regresses to barter"

prior to Mises the best argument against socialism was "look at history", "power corrupts", and the "incentive problem"; then Mises observed:

if the people in charge were benevolent, and they know what what is best, and when the plan is published everyone runs with the program...
and the best planners, get all the best experts, with all the best technology, and situational awareness...

even so there is no way, after the fact, to quantify whether this was the best outcome for society as a whole, or whether it should be tweaked
the market solves this problem with price and profit
market price quantifies value solving the best outcome problem and providing a feedback mechanism

then Mises observed the Austrian Business Cycle

in order to understand how things can go wrong with a market we must first understand why it, if left alone, it goes right:

prices provide signals
interest rates are the price of borrowing
interest rates involve time; a future value of money
the market will determine an exchange rate between money now and money later
artificially low interest rates create a boom, people invest in bad projects
then artificially high rates cause a bust, people go out of business
booms and busts arise from interest rate manipulation and resultant credit inflation or deflation