Most redesigns are judged on taste and shipped in one release. That combination is how stores lose a quarter of their revenue overnight.
They start with aesthetics, not evidence
Begin with session recordings, funnel data and customer objections. The brief should list problems, not moodboards.
They replace everything at once
When every variable changes, you cannot attribute the outcome. Sequence the rollout by template.
They lose the elements that were working
Inventory the proof, guarantees and messaging that currently convert, and carry them forward deliberately.
They ignore technical debt
New themes often add apps and scripts. Set a performance budget before design starts.
They skip the measurement window
Hold the old design available, run the new one on a share of traffic, and let the numbers decide.