Mid-caps sit in the useful middle: big enough to have real businesses, index membership, and borrowable stock, but small enough that a single product line or contract matters. Analyst coverage thins out here, which is where diligence can still pay.
Volatility is a step up. Daily ranges of 3% to 5% are ordinary, and gap moves after earnings of 10% or more are common, so position sizing has to shrink accordingly.
Example: a $5B company with 100M shares at $50 trading 800,000 shares a day turns over $40M. A 20,000-share order is 2.5% of daily volume and can move the price, so it needs working rather than a single market order.
Related: large-cap, small-cap, market-cap, position-sizing