Well, we all know what collecting is… but let’s take a few steps back and keep it simple to start.
Let’s not focus on any real hobbies right now. Let’s pretend there’s a pile of blue circles out there in the world.

Now, somewhere, someone might decide they like blue circles.
COLLECTING WHAT YOU LIKE
We’ve just discovered the first fundamental aspect of collecting: LIKING
If someone collects something they don’t like, the whole collecting situation becomes strange. No matter how far you go in your collecting journey, “collect what you like” is always important.
So we have our collector, liking blue circles… and his collection might look like this:

For some collectors, that’s the end of their story. They like something, and they have a few of them.
If that’s your story, that’s OK. Nothing says you have to go any further. This is Collecting101.com, not “How to Become the #1 World’s Expert in Collecting A Specific Thing”.
KNOWING WHAT’S AVAILABLE
But, most collectors go a little further. They see what’s available, and they notice some differences.

When this happens, collectors may decide they’d like “one of each”.
BUILDING YOUR COLLECTION
Collectors often have a “one of each” goal, a checklist of items they’d like to collect, and a hope to check off each item on the checklist.

The collector may not already have all three colors, so they may seek out the missing ones for their collection. Perhaps the collector can find a shop or another collector who has circles for sale.
Imagine there are circles for sale, arranged on a table for customers:

It is likely that most collectors (and even non-collectors) will quickly recognize that all circles are not equally available. Some circles are plentiful, some appear to be hard to find, and some are in-between. It is likely that circles will not have the same prices.
SUPPLY AND DEMAND
We’ve reached the famous concept of “Supply and Demand”. What does something cost? Usually, it’s a reflection of supply and demand.
The three colors of circles are likely to cost $, $$, or $$$, depending on which color you’re buying because of the supply and demand.

These different prices usually represent how much work (time and effort) will be needed to replace the inventory as it sells. The person selling circles to collectors will probably have no trouble finding more blue circles if they are sold out. They might have a little trouble finding those dark grey circles when they are sold out, and perhaps more trouble finding the purple/magenta circles if they sell the only two in their inventory.
Additional trouble with replacing inventory will cost extra time and effort, and most people realize that extra time and extra effort cost more. Prices are based on supply and demand.
ALL THINGS BEING EQUAL… BUT ARE THEY EVER EQUAL?
Let’s turn our attention back to the simple starting point in this discussion. The blue circles.

Are all blue circles equal? In theory, they would be… but in reality, collectors will usually notice differences. They’re all blue, and they’re all circles, but are they all identical?

Let’s take a closer look…

Upon further inspection, this blue circle has a crack at the top and a missing bit along the edge. All the blue circles are priced at $, but I think I’d like to find one in a little better condition than this one.

Now that I’ve had time to compare, the blue circles aren’t all identical. Some have more damage, and some are in better condition. If they’re priced the same, I’ll take the one in better condition, please… and thank you.
CONDITION AS A FACTOR IN PRICE
Brand new items are usually priced the same. There’s a “manufacturer’s suggested retail price” (MSRP) on cars and refrigerators, and there’s a price-per-gallon on milk and gasoline. The price that’s printed right on the cover of a book is usually the price of the book, when it’s new. But what about when it isn’t new?
Used cars are another matter. How many miles does the car have? How does it look from the outside? How does it look on the inside? Does it have any damage, and if so, what kind? How much damage?
Every car of the same year, make, and model with the same features may have once had the same sticker price in the window, but the purchase price is hard to guess a few years later unless you know the car’s condition. Collectibles are no different.
We took a simple example of different circles with different colors having different prices…

… but the reality is that collectible items which appear to be the same will often have different prices based on the condition.

Once again, this price is a reflection of supply and demand – this time, based upon the supply and demand for the condition of each item.
While it may be very easy to find more blue circles like the example on the left above, it may be very difficult to find more blue circles of higher condition like the example on the right.
As a result, collectors often spend extra when they desire a higher condition, but it is not a requirement. It goes back to a collector’s goals. A collector’s checklist containing “blue circle” can be checked with either of the two examples above. However, it is very unusual for two examples in different conditions to have the same price.
PRICE GUIDES AS A TOOL FOR COLLECTORS
Knowing what is reasonable to spend is important no matter what is being bought. Collectibles or basic essentials, no one wants to spend more than necessary to get what they want.
Price guides are usually helpful as a tool for collectors. It is important to focus on the word “guide” as much as the word “price”. These are not “Price Rules”, but a guide to help determine price.

Perhaps the price guide says $$ but there are lots of them available for $. Don’t overpay if you don’t have to. Perhaps the price guide says $, but the only one available is priced at $$$$. Don’t overpay if you don’t have to… but you might have to!
How badly do you need the item? How long are you willing to wait for a better price? There are no absolute rules for collecting because some collectors may wait and others may not. Some collectors may overpay and others may find amazing bargains.
EACH COLLECTION IS UNIQUE
Each collection is unique, even if it contains all the same items as someone else’s collection. The conditions are likely to be different. The prices paid are likely to be different. The amount of time each collector has been collecting is likely to be different. The places the items were collected and the memories associated with those items are different. Collecting can be a group activity, but no two collections are exactly alike. Speaking of “alike”, let’s end this discussion with a reminder of the first rule of collecting.
COLLECT WHAT YOU LIKE!