Opening ranges by position
Position decides how many hands can be played profitably, because acting last is worth more than any single card in the hand.
The seat a hand is dealt in constrains it more than the cards do. A player under the gun at a nine-handed table has eight opponents still to act, any one of whom may wake up with a better hand or simply decide to attack a range that looks weak. The button has two. That difference is not a detail of etiquette; it is the single largest structural advantage available in No-Limit Texas Hold'em, and opening ranges exist to price it in.
Why late position is worth more hands
Acting last on every postflop street means seeing what everyone else does before committing chips. A marginal holding that would be difficult to play out of position becomes straightforward in position, because the decision to bet, check or fold can be made with more information than the opponent had. The practical consequence is that the same hand carries different value from different seats: a suited connector such as 7-h 6-h is close to unplayable as an early open at a full table and a comfortable raise on the button.
The other half of the argument is arithmetic. An early-position raise has to survive eight players. A button raise has to survive two. Even if every opponent played identically, the chance of running into a stronger hand falls sharply as the seats behind empty out, so the threshold a hand has to clear falls with it.
The blinds are not late position
The small blind and big blind act last before the flop and first on every street afterwards, which is the worst arrangement at the table. It is a common early error to treat the discount already paid into the pot as a reason to play more hands from the blinds. The discount is real, but it buys a seat that will be out of position for the rest of the hand, and the hands that get into trouble most reliably are the ones defended too widely from the small blind.
Adjusting for the players behind
A static range is a starting point, not a strategy. If the two seats to the left are folding constantly, the cutoff and button open wider because the effective table is smaller. If the same seats are three-betting aggressively, the correct response is not to open wider out of stubbornness but to tighten the bottom of the range, since the weakest opens are exactly the hands that cannot continue against a raise.
The discipline worth building is noticing which of those two situations is actually happening. Most players adjust to the aggressive opponent and never adjust to the passive one, and the passive one is where the steadier profit sits.
Working this into memory
Ranges belong in recall, not in reasoning. The point of drilling them with flash cards or board templates is that the preflop decision should cost no attention at all, leaving the attention available for the flop and turn decisions that are genuinely difficult. A player who is still deliberating about whether to open K-s J-s from middle position has spent the budget that should have gone on the turn.