Theory Card 069 — Mental Simulation / Implement
Research lens
Mental simulation is the ability to run the solution in your head or on paper before trusting it. In the Implement stage of BASIC, the goal is to execute the chosen plan in controlled order. That makes this concept especially relevant here, because it shapes how much mental work the candidate is trying to carry at once and what gets made explicit.
Why it matters in SWE interviews
Good candidates dry-run recursion, pointer movement, queue flow, and failure paths instead of waiting for bugs to reveal themselves. Check formalizes mental simulation so it happens consistently instead of only when time happens to remain. In practice, Implement is where the candidate should ask: How do we write or walk through the solution one stable layer at a time? That question acts like a cognitive boundary. It protects the answer from turning into an unstructured search.
BASIC move
A strong move here is to transcribe the plan instead of improvising. For Mental Simulation, that means deliberately naming the important units instead of juggling them implicitly. The interviewer sees cleaner reasoning, and the candidate benefits from keeps execution disciplined and easier to debug.
Common miss
The miss is assuming an answer is correct because it looks elegant. When that happens, the candidate usually feels busy, but the answer is actually becoming less inspectable.
Practice prompt
“While practicing, pause at the Implement step and explain how Mental Simulation changes the way you would handle the prompt.”