How Stock Prices Are Determined

Stock prices in the short run (days to weeks) are primarily determined by flow, positioning, and narrative. When a large fund needs liquidity and sells $500M of a stock, prices decline regardless of whether the business has changed. When a compelling story captures investor attention -- an AI catalyst, a regulatory tailwind, a management change -- capital flows toward it even before earnings confirm the thesis. These short-run forces are largely disconnected from intrinsic value and explain why markets can be volatile and seemingly irrational on a daily or weekly basis.

Over months to a few years, the middle layer of valuation multiple changes and sentiment shifts dominates. P/E expansion (the market paying more for a dollar of earnings) drove much of the 2017-2021 equity market appreciation, while P/E compression (paying less for each dollar of earnings as rates rose) drove much of the 2022 decline. The same level of earnings can be valued at 15x or 25x depending on the macro environment, interest rates, and investor risk appetite. Multiple changes are real returns and losses -- they are not 'temporary' or 'noise' even though they are sometimes mean-reverting.

Over the long run (five to ten or more years), fundamental earnings power and its growth trajectory are what determine whether a stock was a good investment. A company that compounds earnings at 15% per year for a decade will produce strong shareholder returns regardless of the multiple it was purchased at, given reasonable entry valuations. This is the insight behind quality growth investing: buying durable earnings compounders and allowing time to do the heavy lifting reduces the burden on timing and multiple prediction. The challenge is correctly identifying which businesses will actually sustain that growth.

Quarterly earnings releases are the single highest-information-density events in any individual stock's calendar. But what the market reacts to is not the absolute earnings number -- it is the surprise relative to expectations, and more importantly, the forward guidance provided by management. A company that beats Q4 earnings by 10% but guides Q1 below consensus will often fall, because the market is forward-looking and quickly discounts the current period's result in favor of the expected trajectory.

Stock price elasticity to earnings surprises is not constant. In a high-multiple stock trading at 40x earnings, an EPS miss of 5% can produce a 20-30% decline because any slowdown in growth calls into question the entire valuation premise -- the company was valued on aggressive forward expectations, and a miss reshapes those expectations across all future years. In a low-multiple stock at 8x earnings, the same 5% EPS miss might produce a 5-10% decline because the growth expectations were minimal to begin with. Understanding your stock's multiple and what earnings quality it implies is essential for sizing into or through earnings events.

Reflexivity -- the idea that price changes affect fundamentals, which then affect prices -- is one of the most underappreciated dynamics in markets. A rising stock price allows a company to issue equity cheaply, funding acquisitions or investment that improves fundamentals. A falling stock price raises borrowing costs, damages employee morale and retention, and can create customer uncertainty about a company's durability. These feedback loops are most pronounced at extremes: very high valuations enable strategic actions that partially justify those valuations; very low valuations create credit stress that partially validates the pessimism. George Soros formalized this framework; practitioners encounter it regularly in leveraged balance sheets and acquisition-currency dynamics.