Day trading: one or two positions at a time. More than that and you can't manage them at the pace the session demands. Swing: five to eight. Long term: ten to twenty. These aren't laws of nature, but departing from them meaningfully requires a reason, not a habit.

The long-tail problem: every position beyond your best ideas is by definition a lesser idea. A forty-name portfolio necessarily contains twenty mediocre ideas eroding the returns of the twenty good ones, plus commissions and the effort of tracking them.

Positions needn't be equal size. A strong thesis in a quality business at a reasonable price can carry double the weight of a speculative one. But a ceiling stays a ceiling: a single position in a long-term portfolio shouldn't exceed 15–20%, because even the most confident thesis can turn out wrong.

The reverse matters just as much: if a position grows on its own to 35% of the account after a strong run, that is now a new decision. Trimming it back to target weight isn't "giving up upside" — it's risk management.