So if you understand that opportunity cost is in fact about choice and trade off, why did you leave out the core of the principal? Focusing only on the money in this DIY / "pay for it" argument is what make it a fallacy. If you change your car repair example so that Don makes much less per hour than the repair cost. It still might make sense for Don to pay the mechanic to do the repair. Only Don can make that choice. Anyone one else is just giving their opinion.

It's not a post about "The Only Ultimate Way to self-realization". It's a post about "given this statement I often hear, here where it works (and how to improve on it), here where it doesn't". If it doesn't work because of different reasons then:

a. Good, please contribute to the discussion

b. Different reasons resonate with different people. Therefore someone's "core of the principal" isn't the other's.

There is a clear definition for "Opportunity Cost". It's an accepted principal with a long history. From my other comment, I was under the impression that you were not aware of it. Maybe you still aren't. My point is, you are creating the fallacy in your argument by not acknowledging the entire principal. Your use of money as the only driver in the personal decision provides a false conclusion to the "statement you often hear". The conclusion you left me with is: given you're a "High Paid" engineer, you should not fix your own car or help out your community restaurant because the math doesn't work out. However, if you want to screw around with "non-billable" tasks, that's cool, you'll just pay for it.

As almost everyone here has pointed out, that's just NOT what the concept of "Times is Money" is about. BTW, the different reasons ARE the core of the principal. Of course people are going to make different decisions. But, I guess for you it only works when Billable hour > cost of item.

If I may pitch in: since you're trying so hard to throw around opportunity cost, there are, believe it or not, a couple other important points to consider here.

The first is that all valuable things can be measured in terms of other valuable things--including dollars. Opportunity cost tradeoffs of all types can be mapped onto a tradeoff for some quantity of dollars. All things can therefore be measured in dollars, even if you want to be silly and peg the value of things like "true love" as infinite--that's equivalent to infinity dollars. Your time is measurable in money as well.

The second point follows from something either you or someone else noted before. Eventually, paying for things that aren't worth your times adds up, and you have to work more yourself. That's the point! If you can earn more in an hour at work than you would have "earned" by spending an hour painting your house, you make money at no additional expense of time or effort. Alternatively, you could make the same amount of money as you would have gained in house/aesthetic value from painting the house, but spend less time doing it since you are more efficient at work: a time savings. Now, it isn't easy to just "work an extra hour" and get paid for it, but if you make these decisions constantly and trade more time at your job for paying other people to do stuff that isn't worth your time, you'll amass enough saved time to increase your work schedule by a reasonable block.

The key to understanding all of this is that you want to say that the concept of opportunity cost extends beyond money, which it does in a sense--but in another, since all things can be measured in terms of all other things, all opportunity costs have equivalent dollar costs. And so knowing your personal per-hour opportunity cost in dollars is a great way to get a basic quantitative idea of what things are worth your time. If spending an hour with your family is worth more than the $33.74 an hour equivalent that you make at work, it doesn't mean that spending time with your family can't be quantified in terms of dollars; it means that it's worth more than an extra $33.74 but is otherwise difficult to quantify.

And curiously, let's say you reduce your working hours down to 30 a week, the bare minimum you can have to live modestly but comfortably, and spend all the extra time with your family since you love them so much. But why not reduce the hours to 29 a week? Losing that $33.74 every week would put you below the threshold that everyone is happy at. That means that now, $33.74 is worth more than spending the extra hour with your family. In essence, this example shows that the fact that people go to work at all demonstrates how dollar values can outweigh "immeasurable" things like sentimental values, and since they can outweigh, they can be compared, which means that sentimental values have a relative value to marginal dollar value increases or decreases. Therefore, sentimental values can be translated to dollar values. This is a specific case of the general principle noted before, that all things can be measured in dollars, and so it's no sin (and in fact quite handy) to use your dollar/hour opportunity cost liberally when making decisions on how to spend your time.

Really excellent writeup. I think many people are squeamish with the idea of "personal opportunity cost" also because in their experience "personal numeric value"==easy unhealthy way to measure (seemingly) one's worth and to compare two individuals value ("I earn $10/H more so I'm better than him/He earns more so he's better than me"), which can be unhealthy. But it should be approached with as little ego (in the self-worth sense) as possible and as a tool you can use to better self-reflect on your life and your decisions.

Definitely. It's understandable why people dislike these sterile scientific considerations of very real and human problems, but they're incredibly useful. Though romantic notions of things transcending dollar valuation are well-intentioned, they shouldn't get in the way of that utility.

Thank you, you proved my point.