“I increased the contrast to improve usability” sounds reasonable. It still leaves a reviewer guessing which information was difficult to see and why that mattered.
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A stronger explanation is narrower: “The price looked like supporting information, so I increased its contrast and aligned it with the service name. This should make the options easier to compare before selection.” The first sentence describes the change. The second makes a prediction that can be checked.
Give the rationale a point of comparison
Imagine a booking card with a service name, description, starting price and action. Increasing every element would preserve the hierarchy problem at a larger scale. Giving the price more weight is a choice about what people need to compare; keeping the description quieter is part of the same choice.
A useful rationale names both. It also acknowledges uncertainty. If the price varies substantially, making the starting price dominant could create an expectation the next screen cannot meet. Keeping “from” visible and explaining the variables may matter as much as the font size.
Evidence has different strengths
An observed problem, a familiar convention and a personal preference do not carry the same weight. “Three participants missed the fee” is an observation, assuming the sessions support it. “This will increase conversion” is a prediction requiring different evidence. A design review should not quietly turn the first statement into the second.
When evidence is limited, say what informed the choice and what you would check. That gives the team a way to challenge the recommendation without debating your confidence or expertise.
Explain the alternative you left behind
Suppose a table is too wide for mobile. Cards improve readability for individual records but make comparison across records harder. Horizontal scrolling preserves columns but hides information. Neither option wins in every context.
If users mainly open one order to check its status, cards may be appropriate. If they compare several orders by amount and date, the table deserves more consideration. The rationale becomes persuasive because it connects the choice to a task and admits its cost.
You do not need a speech for every spacing adjustment. Spend the explanation on decisions that change behavior, affect implementation or are likely to be challenged. A brief note that lets someone reconstruct your reasoning is usually more valuable than a presentation full of design vocabulary.