I know this is old, but my short reply to those who claim that theory is 'useless' and that they can practice their profession without it is this:
Without the underlying theory, there is no practice.
Why is theory useful?
Theory is the underlying foundation on top of which other things are built. When theory is applied, practice is the result.
Consider computers today. The common computer today is modeled and built on top of the Turing Machine, which, to keep it simple, is an abstract/theoretical model for computation. This theoretical model lies at the foundation of computing, and all the computing devices we use today, from high-end servers to pocket phones, work because the underlying foundation is sound.
Consider algorithm analysis. In simple terms, algorithm analysis and time-complexity theory have been used to classify problems (e.g. P, NP, EXP, etc) as well as how the algorithms we have behave when trying to solve different problems in different classes.
Suppose one of your friends gets a job at some place X and, while there, a manager makes a few simple requests, such as these examples:
Ex 1: We have a large fleet of delivery vehicles that visit different cities across several states. We need you to implement a system to figure out what the shortest route for each vehicle is and choose the optimal one out of all the possibilities. Can you do it?
Thinking the theory is 'useless' your friends don't realize that they've just been given the Traveling Salesman Problem (TSP) and start designing this system without a second thought, only to discover their naive attempt to check all the possibilities, as originally requested, is so slow their system is unusable for any practical purposes.
In fact, they have no idea why the system works at an "acceptable" level when checking 5 cities, yet becomes very slow at 10 cities, and just freezes when going up to only 40 cities. They reason that it's only "2x and 8x more cities than the 5 city test" and wonder why the program does not simply require "2x and 8x more time" respectively...
Understanding the theory would've allowed them to realize the following, at least at a glance:
- It's the TSP
- The TSP is NP-hard
- Their algorithm's order of growth is O(n!)
The numbers speak for themselves:
+--------------+-------+-----------------------------------------------------------------+
| No. Cities | O(N!) | Possibilities |
+--------------+-------+-----------------------------------------------------------------+
| 5 | 5! | 120 |
| 10 | 10! | 3,628,800 |
| 40 | 40! | 815,915,283,247,897,734,345,611,269,596,115,894,272,000,000,000 | <-- GG
+--------------+-------+-----------------------------------------------------------------+
They could've realized at the outset that their system was not going to work as they imagined it would. The system was later considered impractical and cancelled after a significant amount of time, effort, and other resources had been allocated to, and ultimately wasted on, the project --and all because thought "theory is useless".
So after this failure, the managers think "Well, maybe that system was underestimated; after all, there're a LOT of cities in our country and our computers are simply not as fast as we need them to be for our recently cancelled system to have been a success".
The management team blames slow computers as the cause of the project's failure. After all, they're not experts in CS theory, don't need to be, and those who're supposed to be the experts on the topic and could've informed them, didn't.
But they have another project in mind. A simpler one actually. They come the week later and ask say the following:
Ex 2: We have only a few servers and we have programmers who keep submitting programs that, due to unknown reasons, end up in infinite cycles and hogging down the servers. We need you to write a program that will process the code being submitted and detect whether the submitted program will cause an infinite cycle during its run or not, and decide whether the submitted program should be allowed to run on this basis. Can you do it?
Your dear friend accepts the challenge again and goes to work immediately. After several weeks of work, there're no results, your friend is stressed, and doesn't know what to do. Yet another failure... your friend now feels "dumb" for not having been able to solve this "simple problem"... after all, the request itself made it sound simple.
Unfortunately, your friend, while insisting that "theory is useless" didn't realize that the, allegedly simple, request was actually an intractable problem about decidability (i.e. the halting problem itself), and that there was no known solution for it. It was an impossible task.
Therefore, even starting work to solve that particular problem was an avoidable and preventable mistake. Had the theoretical framework to understand what was being requested been in place, they could've just proposed a different, and achievable, solution... such as implementing a monitoring process that can simply kill -SIGTERM <id>
of any user process (as per a list of users) that monopolizes the CPU for some arbitrary/reasonable interval under certain assumptions (e.g. we know every program run should've terminated within 10 minutes, so any instance running for 20+ minutes should be kill
ed).
In conclusion, practice without the theory is like a building without a foundation. Sooner or later, the right amount of pressure from the right angle will make it collapse in on itself. No exceptions.
Do you ever use it in your day-to-day coding?
Yes, but not directly. Rather, we rely on it indirectly. The caveat here is that different theoretical concepts will be more or less applicable depending on the problem domain you happen to be working on.
Surely, we:
- use computers daily, which relies on computational models (e.g. turing machines)
- write code, which relies on computability theory (e.g. what's even computable) and lambda calculus (e.g. for programming languages)
- rely on color theory and models (e.g. RGB and CMYK color models) for color displays and printing, etc.
- Euler's theorems in computer graphics so that matrices can be built to rotate objects about arbitrary axes, and so on...
It's a fact that someone who simply use a plane to travel doesn't need to understand the theory that even allowed planes to be built and fly in the first place... but when someone is expected to build said machines and make them work... can you really expect a good outcome from someone who doesn't understand even the principles of flight?
Was it really a coincidence that, for most of history, no one was able to build a flying machine (and a few even died testing theirs) until the Wright brothers understood certain theoretical concepts about flight and managed to put them into practice?
It's no coincidence. We have a lot of working technology today because the people who built them understood, and applied, the theoretical principles that allowed them to work in the first place.