Why sentiment matters
In efficient market theory, prices should reflect all available information rationally. In practice, the same company with the same fundamentals can trade at wildly different valuations at different moments in time, purely because investor mood has shifted. The Nasdaq traded at a price/earnings ratio above 200x in early 2000 — not because earnings were expected to grow proportionally, but because sentiment was euphoric. The same index traded at 10–15x earnings during the 2009 trough — not because companies had become worthless, but because fear had overwhelmed rational assessment. Sentiment is the distance between price and fundamental value.
Measuring sentiment
Several tools attempt to quantify sentiment. The Fear & Greed Index (CNN Money) uses seven indicators including volatility (VIX), market momentum, put/call ratios, and junk bond demand to score market mood from 0 (extreme fear) to 100 (extreme greed). The VIX (CBOE Volatility Index) measures implied volatility in S&P 500 options — a high VIX signals fearful investors paying a premium for downside protection; a low VIX signals complacency. Investor surveys (AAII Bull/Bear Survey) directly measure how investors say they feel. None of these are reliable short-term market timing tools, but extreme readings often mark turning points.
Contrarian investing and sentiment
A contrarian approach uses extreme sentiment as a signal: buy when everyone is fearful, sell when everyone is greedy. Warren Buffett’s famous dictum encapsulates this: "Be fearful when others are greedy, and greedy when others are fearful." The logic is sound — when sentiment is at an extreme, it often means a one-sided position has been built and most willing sellers (in a panic) or buyers (in euphoria) have already acted, leaving the market vulnerable to a reversal. The problem: markets can stay irrational far longer than most contrarians can stay solvent or calm.
“The market is a pendulum that forever swings between unsustainable optimism and unjustified pessimism. The intelligent investor is a realist who sells to optimists and buys from pessimists.” — Benjamin Graham
What this means for you
Understanding sentiment helps you avoid its worst effects on your own behaviour. Recognise that the temptation to sell is strongest at market bottoms (when sentiment is most negative) and the temptation to buy is strongest at market tops (when everything feels great). The antidote is a rules-based investment approach: regular contributions regardless of sentiment, predefined rebalancing triggers, and a written investment policy statement you can refer to when panic sets in. Sentiment-aware investors don’t try to time the market precisely, but they can use extreme sentiment as a tiebreaker — leaning into equities when fear is extreme and trimming when greed dominates.