cardinal rule.

relationship between short odds and pot odds.

When you have a hand that requires improvement in order to have a good chance of winning the pot the cardinal rule in Texas hold 'em is that if the pot odds are equal to or better than cardodds, you should invest money.
Ex. if you have HJK-hjQ at hand and that the board is 10-3-J-7 of colors that makes it impossible to flush. Will there be an ace or a nine on the last card you probably win the pot with a stright. If there are 175 in the pot when the two players after the blinds are operated opening 50 and called 50
Short odds are 38 (the unknown cards remaining, which does not give you the stright) to 8 (the card that gives you the stright) or 4.75 to 1.
Pot odds are the one currently in the pot (175 50 50 = 275) against what it costs you to call (50) or 5.5 to 1.
Pot odds are better than short odds and it is justified to call.
However, one must keep in mind that the cards will help you perhaps help someone else so that she gets a higher hand.
Eg so reduced the value of a strightdraw if there is a possible flush draw. A quarter of the cards that give a stright can also give someone else a flush.
If there exist two cards that are better suited to the table than what you are doing, so can an opponent have these cards.