The answer isn't the retail investor. Not you buying 50 shares from a mobile app. Stock prices are moved primarily by institutional investors: mutual funds, ETFs, hedge funds, insurance companies, pension funds, and investment banks. These entities operate with hundreds of millions or billions of dollars. When a fund decides to build a position, it doesn't buy in a single order — it buys over days or weeks, gradually, to avoid moving the price against itself.
Price as the Result of Supply and Demand
The price of a stock at any moment is simply the last price at which a buyer and a seller agreed to transact. There's no "true" or "correct" value — there's a market price that reflects the consensus of all participants at that instant.
When there are more buyers than sellers at the current price, the price rises. When there are more sellers than buyers, it falls. The mechanics are simple. What makes them complex is understanding who those buyers and sellers are and why they act when they do.
A pension fund managing $50 billion that decides to increase exposure to a specific sector may buy over several weeks. That sustained buying pressure gradually pushes the price higher. The investor who reads a headline about that sector two weeks later and decides to buy arrives late — paying a higher price, after the institutional flow already drove the move.
Liquidity: Why Not All Stocks Are Equal
Liquidity is how easily an asset can be bought or sold without the transaction itself moving the price. A highly liquid stock — Apple, Microsoft, NVIDIA — can absorb millions of dollars in orders without the price shifting significantly. A low-liquidity stock can move 3% on a $50,000 order.
For individual investors, this matters for two practical reasons. First, low-liquidity stocks are more vulnerable to artificial moves. Second, the bid-ask spread — the gap between the buying price and the selling price — is wider in illiquid stocks, representing an implicit cost on every trade.
Market Makers: The Role of the Intermediary
Market makers are institutions with a contractual obligation to provide continuous liquidity in certain markets. They always have buy and sell prices available, even when there aren't enough natural buyers and sellers facing each other directly. In exchange for taking on that inventory risk, they keep the spread.
This explains why spreads widen at market open or during unexpected news events: market makers are managing more uncertainty and adjust their prices accordingly.
Volume as the Trail of Institutional Money
A fund that wants to build a $200 million position can't place a single $200 million order. That would immediately move the price against it. Instead, it splits the operation into hundreds of smaller orders distributed over time.
This process leaves visible traces. Days when volume is abnormally high while the price advances with conviction indicate a large buyer absorbing selling from those who want to exit — this is called accumulation. Days when volume is high while the price gives ground with weak bounces indicate distribution: institutions reducing positions gradually.
A price breakout with volume two or three times above average carries far more credibility than the same breakout on normal volume. In the first case there's institutional money behind it; in the second, probably not.
What This Changes for the Individual Investor
Understanding that institutions move prices and retail reacts has a direct implication: the individual investor's edge isn't in processing news faster but in detecting patterns of institutional accumulation before they become obvious to everyone.
That's what a systematic scanner does. It doesn't filter headlines or analyze CEO statements: it detects price and volume signals suggesting institutional capital is moving in a direction. It doesn't guarantee the move will continue, but it identifies situations where the risk/reward is reasonably favorable according to objective, reproducible criteria.
The investor who understands who moves the market starts asking the right questions: not "what do the headlines say?" but "what do price and volume tell us about what institutions are actually doing?"