There are only four main professions in the world; all other industries are variations of these four. **Prostitute Type:** Clients pay voluntarily; information is transparent. Examples include catering, hairdressing, and housekeeping. The money paid and the service received are essentially equal, with little information gap. **Robber Type:** Clients do not pay voluntarily; payment is made through coercion or monopoly. Examples include monopolistic platform fees and hidden bundled charges. Payment is not based on information gaps but on power differences. **Thief Type:** Clients are unaware of hidden payments. Examples include internet platforms trading privacy for profit and hidden financial fees, quietly reaping profits without your knowledge. **Scammer Type:** Clients believe they are paying voluntarily but are actually misled. Examples include "IQ tax" health products and pseudo-scientific courses, exploiting cognitive biases to create illusions and make you willingly hand over your money. The heartbreaking truth is that ordinary people rarely make big money in the prostitute type of business. Those who truly achieve high returns with low investment are often the thieves and scammers. In essence, money is about exchange, and the gap between emotion and reason is the source of high profits. All the mysteries lie in the human heart—grasping people's inner fears and desires is the key to making money.