Identify the level of the question
'Why did you do that?' can refer to a business goal, an engineering constraint, or your personal judgment. Do not repeat the entire story. Briefly check your understanding and answer the relevant layer. When the question is ambiguous, one clarification can save a long detour.
Lead with your judgment, then the evidence
Try: 'My decision was… The main reason was… The cost was…' When comparing approaches, focus on the constraint that actually drove your choice. A list of generic advantages is less convincing than one specific comparison from your project.
Make room for what you do not know
If you did not test at a particular scale, say so. Explain what you would measure first, where you suspect the bottleneck lies, and what evidence would change your view. Keep established facts separate from hypotheses.
Find the point where your answer lost focus
After practice, find the sentence where you started repeating yourself, avoiding the question, or listing terminology. Decide whether you need more knowledge or a clearer order. The first needs investigation; the second may need a stronger opening sentence and one concrete example.