This is a model I made on Vensim. Vensim is a modeling software. The model shows how the main aspects of selling, buying, growing, and distribution of cactus are related. The goal was to figure out how much cactus would have to be produced in order for the business to become profitable. 

Though the model looks complicated and confusing from afar, a closer look will reveal that each individual connection makes sense. Look at the "Welfare" graph. If the supply is high and the price is low, the people are happy. If the supply is low and the price is high, the people are unhappy. As some of the current stock of cactus decay, the profit goes down. The amount in the stock is determined by the demand and supply, and the amount of stock determines the sales. The stock has a decay, surplus and deficit, meaning that after the growing season some of the cactus is stored. Some of the cactus is lost (decay) some is extra (surplus). Sales in tons are converted to profit in dollars. Profit is determined by the sales and the price of cactus and decreased by the cost of growing the cactus and the cactus lost during the year due to varying factors.