The demand curve is the willingness-to-pay distribution of your market
A willingness-to-pay (WTP) curve shows the number of customers willing to buy at each price. At $10, maybe 10,000 people buy. At $20, 7,000 buy. At $50, 2,000 buy. At $100, 200 buy. The curve slopes downward and rightward, a fundamental law of demand. The area under this curve represents total possible revenue: selling to all 10,000 at $10 yields $100,000. Selling to 2,000 at $50 yields $100,000. Selling to 200 at $100 yields $20,000. The same product, same people, different revenue based on where you price. The shape of the WTP curve (steep or gentle, cliff or gradual) determines the optimal price point. A steep curve means many customers have similar WTP; a gentle slope means WTP is spread across a wide range.
Price discrimination captures more of the area under the curve
If you could charge each customer their maximum willingness to pay, you'd capture the entire area under the curve (perfect price discrimination, impossible in practice). In reality, you choose one price and sell to all customers willing to pay at least that price. Some customers pay less than they would have been willing to; this is consumer surplus, the difference between what they'd pay and what they actually paid. Businesses with multiple products, tiers, or customer segments recover some of this surplus through packaging (bundling high-WTP items with low-WTP items) or segmentation (charging different prices in different markets). The closer a company can get to matching prices to individual WTP, the more revenue it captures.