As a junior, how do you explain msg.sender and trust boundaries confidently in Solidity interviews?

My mentor had this annoying but brilliant rule — every line I wrote had to start with “because I trust X.” At first, I rolled my eyes. But within a week, I saw how many invisible assumptions lived in my code. I trusted msg.sender without context. I trusted arrays wouldn’t overflow. I trusted users to behave. All wrong. That one exercise built my security reflex. Now, before every commit, I check: “Where am I trusting something blindly?” It’s amazing how often logic flaws hide in those tiny gaps. Juniors who learn this early save their teams from nightmare audits later.

My biggest mistake early on was assuming people use contracts the way I intended. I once told myself, “No one will ever call this twice.” Someone did. That broke the whole state flow. From then on, I started treating every function like a public doorway an attacker might abuse. Threat modeling, for me, became less about frameworks and more about paranoia in small doses — question every state change, test weird sequences, and simulate what a malicious user might do. That shift made debugging fun again. It’s not about fear, it’s about predicting chaos before it hits mainnet.

I think of threat modeling like chess. Every move you make has an opposite counter waiting. When I review a smart contract, I visualize it like a board, if a function changes ownership, what else breaks? If you delay execution, what state gets exposed? That habit made complex DeFi contracts much easier to reason about. It’s also how I calm juniors who think security is just paranoia, it’s not. It’s controlled imagination. The more you think in moves and counter-moves, the less scary audits feel. You don’t need to be a senior to model threats; you just need curiosity and repetition.

When I was a junior, I used to treat pull requests as just “code ready for review.” Now, every PR I open has a small note at the end “Risk if called unexpectedly.”

Initially, I added it just to sanity-check my own logic. But over time, reviewers started engaging with it, pointing out edge cases, improving the reasoning. It turned our reviews from defensive back-and-forths into genuine collaboration.

That one line makes you pause and think:

What if this function gets triggered twice?

What if the owner’s key is compromised?

What if gas runs out mid-call?

Seeing your own code through an attacker’s perspective changes how you write.

If I could give one piece of advice — threat modeling isn’t about writing flawless code; it’s about making your assumptions visible so others can validate them faster. That’s how you build real security culture in a team.

Love this mindset. Threat modeling is not just for auditors. it’s a habit that shows accountability. Even listing who controls state or value helps teams trust your code review process. For anyone exploring audit thinking, start with this thread on common smart contract security mistakes → https://artofblockchain.club/discussion/how-to-answer-common-smart-contract-security-mistakes-in-blockchain-auditor-interviews

Also check how contracts are actually audited and verified → https://artofblockchain.club/discussion/can-smart-contracts-be-audited-what-are-the-common-tools-for-auditing