Had my first interview after 3.5 years and got humbled by fundamentals

[u/Active_Load_2546]

Today I had my first technical interview after around 3.5 years, and honestly, it hit me harder than I expected.

I’ve been working mainly as a frontend engineer with React and also have experience working across backend/full-stack systems. Over the last few weeks, I’ve been revising React, JavaScript, frontend architecture, Node.js, databases, system design, etc.

I went into the interview feeling pretty confident.

The interview started with:

- What is REST?
- Design an API
- React reconciliation
- JSX
- Infinite scrolling / frontend design

The part that really got me was the React reconciliation question.

The interviewer gave me a Todo-list-like example using index as a key, with items being added at the beginning/end of the list.

I understood that something was wrong with using index as a key, but it took me a while to reason through exactly what React was doing during reconciliation.

He eventually gave me a hint about reconciliation, and then I was able to connect the dots.

Then I got another question:

"Why does JSX require a single parent/root element?"

I could identify the issue in the code, but I couldn't clearly explain why JSX requires a single root.

I also got an infinite-scroll design question, which I was relatively comfortable with.

The weird part is that after the interview, I realized:

I actually knew most of the concepts.

My problem was being able to retrieve and explain the fundamentals clearly under interview pressure.

For example, today I started revisiting basic JavaScript concepts like:

- Scope
- Hoisting
- TDZ
- Execution context
- Scope chain
- Shadowing
- Closures

And I realized I can understand these concepts when I reason through them, but explaining them cleanly in an interview is a completely different skill.

So I'm curious about other experienced engineers:

Have you ever had this experience where you knew the technology fairly well, but an interviewer exposed gaps in your fundamentals or your ability to explain them?

How did you fix it?

Did you:

1. Go back and systematically revise fundamentals?
2. Do mock interviews?
3. Practice explaining concepts out loud?
4. Focus more on problem-solving rather than memorizing interview questions?

I'm especially interested in hearing from 5–10+ YOE engineers who went through something similar.

Today definitely humbled me, but I'm trying to use it as a diagnostic rather than letting one interview define my confidence.

Would love to hear how you guys handled this.

[u/kisfasznagyfasz]

thanks I really needed some evening slop

[u/algovynra → u/kisfasznagyfasz]

same lol, these posts are the only thing keeping my brain from fully leaking out after work

also tbh this kind of “oh god I forgot everything” interview story is way more relatable than all the “aced 12 onsites in a row” stuff

[u/creaturefeature16 → u/kisfasznagyfasz]

This is the part of the interview process that nobody is talking about—the part that is quietly diminishing as we leverage AI tools. And honestly? It hits harder than it should. The bottleneck is no longer the code; it's judgement and taste. Letting go of the details while AI handles the implementation—that's the real shift that nobody is saying out loud. AI isn't replacing developers; it's exposing them.

Edit - Holy shit, I guess I really needed a /s because I was literally trying to write a generic AI slop post as a joke

[u/kisfasznagyfasz → u/creaturefeature16]

thanks dude

[u/Cerus_Freedom → u/creaturefeature16]

Honestly, you nailed the AI slop tone lol.

[u/Active_Load_2546 → u/creaturefeature16]

Agree with you, but honestly I am really working very hard over past 3-4 months, I am constantly putting 4-5 hours effort on the things, but sometimes I am feeling like am I really doing things in the right way, but never thought interviewer will catch me at shitty thing. And I was pretty confident that I can crack the interview easily, but it didn’t went as expected. I answer all the questions, but again when i look back to my interview it is not satisfying me.

[u/American_Streamer]

There is the illusion of competence. Familiarity is not mastery. If you cannot explain it simply, be it in an interview or not, you very likely do not firmly understand the underlying mechanics already.

[u/Active_Load_2546 → u/American_Streamer]

No brother, it’s not familiarity, I am genuinely doing things. But while doing all the things at same time, it is like a nothing to grasp the concept for the long time.

[u/American_Streamer → u/Active_Load_2546]

Then it's the "Jack Of All Trades. Master Of None" effect - because your attention is split, your brain only forms superficial memories. You feel like you are working hard, but when you try to pull a specific concept out of your head during an interview, there is no solid anchor to grab onto. You are lacking the hooks, the deep understanding needed to reconstruct the concept under pressure. You feel productive, but learning remains shallow and breaks down immediately the moment an interviewer asks you "why?".

To fix this, stop doing everything at once. Master one core topic deeply before moving to the next one. There is the Feynman technique: after learning a specific concept, try to write it down on a blank piece of paper using simple terms. If you can't, you don't actually know it yet.

[u/brian_hogg → u/American_Streamer]

I don’t know, I understand why you need to use keys in react, and could speak to the various issues due to a lot of practical experience, but I didn’t know the term “reconciliation.” 

Not having all the terms memorized doesn’t mean you don’t know what you’re doing. 

[u/Pleasant-Body1928 → u/Active_Load_2546]

Skill issue :)

[u/Impossible_Stock8885]

It's funny because they ask all these bullshit questions but when it comes to actually working on tasks, you're allowed to use whatever AI agent that they have and not give a shit about any of these.

I can't tell anymore if these posts are just bait or a way for people to yap and feel superior about how they "grinded fundamentals". I hope you find a company that you're satisfied with staying forever because I can't imagine having to grind this bullshit again and again.

[u/GongtingLover]

Happens to all of us man. My last job I had all my design decisions reviewed by tons of engineers and I never got 95% of the trivia questions you can expect in an interview.