"Holy metaphorical connundrum Batman!" the Boy Wonder exclaimed exclaimingly, "how can we emphasize the point to the client without yet another mis-appropriated allusion that he doesn't understand?"
"I'm not sure," replied the Caped Crusader pondering the ponderable in a pensive manner. "Though perhaps…"
He spun and confronted the Capracious Client
"it's easy you villanous fiend," intoned the black masked hero, "building your site is like constructing a house. All houses are built differently though many of them use an exact same pattern and the same pre-fabricated parts and construction methods and…"
"Holy wandering allusion," moaned Robin as yet another metaphor rained down like a house on fire.
Okay, so we've all been there. You build a framwework for the client who is prepared to waste months to-ing and fro-ing a design based on just the right shade of vermillion to a bunch of low-life interface skinners (like me); comfortably burning into both the budget and the time to complete the project when you come to the final pieces.
These can be anything from the shipping model to the shopping cart or payment processor, or perhaps it is the packaging types – it doesn't matter. What does matter are the words: "heck, every business like mine has one of these, why can't we buy something 'off the shelf' or adapt an existing one?"
Now you know the answer is really quite simple, and as you mentally put the hammer quietly down and reconstruct the clients mangled body in your thoughts, you smile politely and try to explain it to them.
Except of course you cannot.
Well…. you can….
You can tell them about data models and hooks to code and logic processes and the many other elements that have been custom built and uniquely implemented onto their pretty interface to actually make the site work (using the new way they required), and then you could get a bucket and scoop the melted remains of their brain into it and funnel it back up their nose.
Or you could search, as our eponymous heroes might, for the next best thing, a real-world metaphor or allegorical situation to give them. Except, like many prophets have found, these do not always work. I always liked the parable of the lost sheep myself, go away do wtf you like as long as you return right at the end and say sorry I love you God, you're safe. Hamlet hated that clause. But it does show that a message can be lost as it is not always the allegory that's wrong it is how people interpret it.
So what can we do, well the answer is not a lot really. Search for the best allusions and metaphors we can and share them is about the best I can come up with. So here we go, an I have thought of and seem interesting as to why custom elements have to be used even if there is similar technology to be bought 'off the shelf' so to speak. If I think of more I'll let you know.
Imagine that every site is in fact a gold mine (or diamond/steel whatever you like), now the mines all use the same techniques for digging, the same tools and the same processes for extracting their ore and they all use conveyor belts for transferring that ore and pumps to keep the mine dry. But, they are all different shapes, in different rock and at different depths, so the mining companies do not in fact buy standard conveyors and standard pumps and adapt them, as they will either end up with more than they need which is wasteful or end up with an inadequate solution. Both of these will result in lost profits or dead miners, both of which are disastrous. So mines have custom built conveyors and pumps, the principles are the same but the exact equipment is different.
You can even use a real world example of this to explain why sometimes it takes so long to fix or ammend custom created code by referrring to the refurbishment of the London Underground escalators which took many years as the originals were very old and were custom built to size and purpose.
Some shops and mass produced buildings do have standard fit designs, but these are generally less-favoured both by architects and engineers as they are an unwelcomed compromise in terms of creativity and flexibility of design and construction.
If you start to compromise your entire construction just to use regular repeated elements you will not only build an inadequate item but will suffer from looking like every other of that type in existence and loose the edge of being individual.