Drawdown

The decline from an investment's highest point to its lowest point before it recovers.

Example

An index that falls 35% from its peak before turning around had a 35% drawdown.

A large drawdown needs an even larger gain to fully recover from - a 50% drawdown needs a 100% gain just to get back to even.

Volatility — How much and how often an asset's price moves, up or down, over a given period.
Permanent loss of capital — Money that is gone for good - the business failed, the asset became worthless, or it was sold at the bottom and never bought back.

Nothing arrives while you wait, and the wrapper sets the tax — Large declines with no income to cushion them, a running charge on an asset that pays nothing, a roll cost that hides inside a price - and in the United States, three wrappers around the same metal taxed three different ways. (12 min)
Total loss is an outcome here, not a tail — Four separate routes lead to zero, none of them exotic. Then the volatility arithmetic, the costs nobody totals, and a tax treatment that can leave a bill in currency against a position that has already fallen. (13 min)
Rebalancing: returning to the plan — Left alone, a portfolio drifts towards whatever has done best - which is the same as drifting towards a bet on the recent past continuing. Rebalancing is the small, unpleasant act that undoes it. (9 min)
Leverage: the same asset, a different outcome — Borrowing to invest does not change what you own. It changes how far the asset can fall before the decision is taken out of your hands. (11 min)
Concentration: one thing going wrong — Concentration is how fortunes are made and it is how they are lost, and the two facts are the same fact viewed at different times. (10 min)
What a portfolio is actually for — A portfolio is not a collection of good ideas. It is an instrument built to deliver specific amounts of money at specific times, and almost every construction question becomes answerable once that is written down. (10 min)