The three-opening repertoire
As White, one first move and a plan against each main reply. As Black, one defence to 1.e4 and one to 1.d4. That is genuinely the whole requirement for the overwhelming majority of games you will ever play, because 1.e4 and 1.d4 together account for the large majority of first moves at every level below master.
The other first moves — 1.c4, 1.Nf3, 1.b3 — do need an answer, but not a separate repertoire. Most of them transpose into positions you already know, and a sensible developing setup handles the rest.
Why more is worse
Opening knowledge decays unless it is used, and the currency is repetitions. Six openings means each one comes up half as often, so each decays twice as fast, and you spend your study time re-learning rather than deepening. The player with three well-worn openings reaches familiar positions constantly; the player with eight is a beginner in all of them, permanently.
There is a second cost that is easy to miss. Playing the same structure repeatedly teaches you the middlegame that follows from it — which pieces to trade, where the breaks come, what the endgame looks like. That transfer only happens with volume. Spreading across many openings buys variety and forfeits the lesson.
When to add a fourth
Add one when a specific opponent keeps beating you in a specific position and you have already tried to fix it inside your existing repertoire. Add one when you are genuinely bored, because a bored player studies nothing at all and a fresh opening is cheaper than a lost habit. Add one when you have reached the level where opponents prepare against you — which is much higher than most people assume.
Do not add one because you lost a game. That is the reason that produces a repertoire of eight openings and command of none.
Frequently Asked Questions
Do I need a different opening for blitz and classical?
No, and having one usually hurts. The same opening in both means every blitz game is a repetition of your classical preparation, which is free practice. Some players do pick sharper lines for blitz where the clock does the work, but that is an optimisation, not a requirement.
What should I play against 1.c4 and 1.Nf3?
In most cases, the setup you already play against 1.d4. Both moves frequently transpose, and where they do not, a solid developing scheme with pawns on d5 or e5 gives a normal game. It is not worth building a dedicated repertoire for first moves you will meet a handful of times a year.
Is one opening as Black enough for both 1.e4 and 1.d4?
There are universal setups that try, and they save real time, but they cost you something against precise play — the same scheme cannot be equally well-placed against two different centres. One defence each is the better trade for most players, and it is still only two things to learn.