When a plant deteriorates, the most recent change often gets blamed. A short timeline can reveal that several changes happened together: a new pot, a darker room, extra feed and more frequent watering.
Write down what happened and approximately when. Include changes in heating, weather and the plant's position, even if nobody deliberately altered its care.
Choose the next step from evidence
Inspect the root area, stems, leaves and drainage. Correct an obvious urgent problem, such as water trapped in a cover pot, before adding another product.
Where the cause is uncertain, avoid changing every condition at once. Keep photographs and note what you adjust so the plant's response can be interpreted.
The timeline is particularly useful for a newly purchased plant. Record its nursery conditions where known and what changed when it arrived home. A plant does not experience 'indoors' as one uniform environment. Its light, temperature and drying rate can change substantially between two nearby rooms. A care history turns that vague move into something you can investigate.
The RHS guide to leaf damage lists several possible causes of similar symptoms, including watering and environmental changes. A timeline helps organise those observations; it cannot diagnose a disease on its own.
Related reading: Common Plant-Care Mistakes: Watering, Feeding and Repotting.