Is most plainly visible when spending more money on one thing means that less money can be spent on anther thing?

I believe the answer is opportunity cost.

Opportunity cost refers to a certain choice that we need to sacrifice in order to choose another choice.

For example, you have $50 that you could use either on date with your girlfriend or to buy your favourite game. If you choose to use that money to go on a date with your girlfriend, the unability to buy the game is the opportunity cost for you.