If they understand their friend's work deeply, doesn't that imply they've done something comparable themselves?
Basically, they volunteer technical challenges they're aware of while simultaneously telling you what the high level solution is. But then you put a terminal in front of them and ask them to set up Postgres in a star schema with some dummy data, and then to write a query joining the two tables they were talking about before. Despite Postgres being on their resume, they'll completely flounder and not even know they need semicolons to terminate commands. Their joins won't just be wildly inefficient, they'll be syntactically incorrect and refuse to run. They won't be able to create, insert, select, truncate, drop, etc. They don't know how to create an index and can't mention any of the options for indexing, let alone the default provided by Postgres.
Keep in mind this example is just meant to be illustrative. Thinking through how to fix the scenario might not generalize to all the ways this can manifest. The kernel of how this arises is a person like so:
1. They read a lot about technical solutions at a high level. They can follow that if you have problem A then you need, roughly, solution B.
2. They have no contextual flexibility or practical foundation for understanding their solutions. They might have read Designing Data Intensive Applications, but they can't actually code and have never administered a database. To the extent they understood the book, they only internalized low hanging fruit.
3. They are charismatic, or ar least comfortable talking about technical topics. They will try to lead the conversation as much as possible, which is where you see them volunteering technical challenges and then offering solutions. But if you force them to answer heavy technical questions which drill deep into a specific area, they'll probably try to zoom back out.
That's what that asshole is looking for. :)
Though to be fair, if you come up with that strategy and can't do -anything- at a sql console, I'm going to ask how you normally interface with the database, because that's like a Linux expert not knowing how to use tar or ls or something.
As for the Linux/tar piece, I've used Linux on desktop for a few years(both Ubuntu & Fedora) & have used Suse and CentOS for servers for much longer.
I can tell you tar means tape archive. I can tell you I mostly use it with gunzip to compress it. I still google/reverse terminal search what flags to use with it both when archiving it and unarchiving it. I could probably remember some flags if I spent enough time thinking - why would my brain waste that much effort though?
I don't work as a backup administrator. I have better things to worry about knowing/having present at the forefront of my (admittedly human sized) memory.
Do you suppose you could have made this point without calling me a name?
If you can explain how to design a system and you can do it, but don't know the exact commands off the top of your head, my comment isn't describing you. I don't expect people to e.g. know awk like the back of their hand, or to write perfectly compiling code on their first try.
But even if you don't have perfect recall of the commands, it should be pretty clear whether or not you've ever opened an editor and done basic implementation. If the GUI is your thing that's fine. But your knowledge must have some practical foundation which demonstrates you can actually walk the walk.
edit: yeah upon re-reading you’re talking about completely obvious lack of practical experience... fair point
Imagine you're interviewing a candidate and they're talking through how to design an analytics service. They begin talking about e.g. database architecture, and how this type of data is most appropriate for a star schema. They start talking about the tradeoffs of row versus column orientation. They mention they'll need to do indexing for performance and talk about the index space versus query speed tradeoff. They say they'll do joins on the x and y tables.
Is this demonstrating deep understanding though?
Basically it's like someone else said. They read a book and know a lot of answers, but they can't do the most basic implementation of a solution.
No, it seems about on about the same level as being able to paraphrase the abstract of a paper about the system. I would not take it as showing that someone has read past the first page. A high-level overview just isn't enough for that. You have to ask your own probing questions too. Limiting the conversation to the particular problems they bring up is essentially taking them at their word when they claim to be skilled. I've seen lots of occasions where trying to drill down for a bit more detail on some part of what they talked about consistently came up empty (without going anywhere near sitting down at a computer to write a fizzbuzz equivalent).
Even though the whole thing could be very simple. Another thing is, they will come up with reasons that the issues with the user story/task for code/solution is due to environment or some other reasons like tools, framework, scalability and "bs".
Look at it this way. I was able to understand all of the maths proofs taught at my degree, but I could not have come up with them myself.
Imagine putting a math problem in front of someone and asking them to solve it. They correctly identify it as a system of linear equations. They volunteer that they would solve it using x algorithm which has a time complexity of y.
Then you ask them to actually solve it, and they can't even make the first movement towards doing so. They mentioned LU decomposition, but they can't even do Gaussian elimination on paper. They don't know what elementary row operations are. They can't obtain an augmented matrix or put it into (reduced) row echelon form. They don't know anything about linear independence or the rank of a matrix. You put an inconsistent system in front of them and they keep banging away at it, determined to find a solution...etc.
That's what it's like interviewing one of these senior engineers. It's surreal - they confidently pattern match the problem using limited heuristics, and they toss away low hanging fruit to demonstrate knowledge. But when you ask them to do something practical and specific, they either refuse and zoom out into abstract-land again, or they hopelessly fail.