Do you fix your house one time and you're done?
Of course not.
Having a house is having constant maintenance.
When we moved in, we bought a new roof.
And then added insulation to the attic.
And then got all new toilets.
And we've had constant handiman work done along the way.
And plenty of plumbing issues as well and some pressure cleaning.
Then new outdoor lights.
New garage door opener.
Then a new swimming pool.
And now a new air conditioner.
Soon we'll need a new water heater as well.
And then we'll start with the kitchen, with the fridge, stove and microwave.
Then we'll need carpet, and perhaps have the walls painted.
It never ends.
So you take a custom application built by a contractor.
You get the specs from the customer, have a contractor build it, test and move to production.
And the consultant goes away.
Project is done, right?
That's when the maintenance begins.
Because you will have bugs after go live.
They may have missed some of the logic.
You're going to want increase functionality.
And merge the data with some other data.
And of course reports.
So you may now have a full time resource maintaining this new application.
Which brings additional costs and time and resources.
So when you budget the cost of a new application, you'd probably want to at least double the price to include maintenance cost.
Buying or building the product is only half the battle.
The other half is the maintenance.
Don't get caught flat footed assuming you're done once the product moves to production.
And there you have it!