There’s a heuristic at work here which isn’t completely unreasonable.
I buy $15 items on a daily basis. If I form a habit of ignoring a $5 savings on such purchases, I’ll be wasting a significant fraction of my income. I buy $125 items rarely enough that I can give myself permission to splurge and avoid the drive across town.
The percentage does matter—it’s a proxy for the rate at which the savings add up.
It’s also a proxy for the importance of the savings relative to other considerations, which are often proportional to the value of what you’re buying. If you were about to sign the papers on a $20000 car purchase, would you walk away at the last minute if you found out that an identical car was available from another dealer for $19995? Would you try to explicitly weigh the $5 against intangibles such as your level of trust in the first dealer compared to the second, or would you be right to regard the $5 as a distraction and ignore it?
But if the time to drive across town is worth more than $5 in the $125 case, it’s worth more than $5 in the $15 case, and forming that habit loses big. (Unless driving across town once allows you to save on more than one item, but that completely breaks the example.)
Other than cognitive cost, I don’t see any reason to speak in terms of habits rather than case-by-case judgments here.
In the car case, you know the cost of walking away is very high; this screens off the informational value of the price.
It seems to me like it shouldn’t matter how often you buy the $15 items, technically. Even if you always bought $125 items and never bought $15 items, your heuristic still wouldn’t be completely irrational. If you only buy $125 items, you’ll only be able to buy 4% more stuff with your income, as compared to 33% more stuff if you always buy $15 items.
There’s a heuristic at work here which isn’t completely unreasonable.
I buy $15 items on a daily basis. If I form a habit of ignoring a $5 savings on such purchases, I’ll be wasting a significant fraction of my income. I buy $125 items rarely enough that I can give myself permission to splurge and avoid the drive across town.
The percentage does matter—it’s a proxy for the rate at which the savings add up.
It’s also a proxy for the importance of the savings relative to other considerations, which are often proportional to the value of what you’re buying. If you were about to sign the papers on a $20000 car purchase, would you walk away at the last minute if you found out that an identical car was available from another dealer for $19995? Would you try to explicitly weigh the $5 against intangibles such as your level of trust in the first dealer compared to the second, or would you be right to regard the $5 as a distraction and ignore it?
But if the time to drive across town is worth more than $5 in the $125 case, it’s worth more than $5 in the $15 case, and forming that habit loses big. (Unless driving across town once allows you to save on more than one item, but that completely breaks the example.)
Other than cognitive cost, I don’t see any reason to speak in terms of habits rather than case-by-case judgments here.
In the car case, you know the cost of walking away is very high; this screens off the informational value of the price.
It seems to me like it shouldn’t matter how often you buy the $15 items, technically. Even if you always bought $125 items and never bought $15 items, your heuristic still wouldn’t be completely irrational. If you only buy $125 items, you’ll only be able to buy 4% more stuff with your income, as compared to 33% more stuff if you always buy $15 items.