Justify Building an In-House System Instead of Adopting an Existing Solution

In the hiring manager round, you describe a past project in which your team built its own system. The manager pushes back: the industry already has solutions that could do this job, so why did you reinvent the wheel instead of adopting one of them? Answer as you would in the interview, using a real project of your own. ```hint Make the alternatives real Name the specific existing options you evaluated and the concrete criterion each one failed, rather than a general claim that none of them fit. ``` ```hint Building has a running cost Account for what the in-house system costs to run and maintain over time, not only what it saved at the start. ``` ### Clarifying Questions - Is the manager challenging the decision itself, your part in making it, or both? - Is it acceptable to talk about a decision you inherited and later had to defend, rather than one you made? ### What a Strong Answer Covers - The specific alternatives that were evaluated, and the decision criteria: scale, cost, fit to requirements, integration and control - Evidence behind the decision, such as a benchmark, a proof of concept or a cost model, with numbers - An honest account of what building cost and risked, including maintenance and on-call load - Clear ownership of your role in the decision and of the technical challenge itself - Reflection: what you would do differently, and the conditions under which you would now buy instead ### Follow-up Questions - Half-joking, the manager asks you to be honest: was the technical challenge you described actually solved by an AI tool? How do you answer, and what makes your answer credible? - If a mature open-source or vendor product with the same capabilities appeared today, would you migrate? What would the migration cost? - What did the in-house system cost to operate in its first year compared with your original estimate? - Who disagreed with the decision to build, and how was the disagreement resolved?