Though the sun shines, leave not your cloak at home.

Understand the thought

Meaning in plain English

Favourable conditions now do not remove the value of reasonable preparation for a change. The cloak image encourages a proportionate precaution, rather than expecting every pleasant situation to turn bad or carrying every possible safeguard.

What the words are saying

The sunshine makes the cloak seem unnecessary at the moment of departure, yet the saying advises taking it. The image distinguishes present comfort from the conditions that may arise later. Applied to an undertaking, it encourages a manageable backup when circumstances can change and the preparation has a clear purpose. It does not predict a particular weather event or require constant fear of what might go wrong. Precautions can themselves have costs and limits. The useful question asks what change is plausible, how much it would matter and which preparation is proportionate, rather than treating a favourable start as complete evidence about the rest of the task.

Everyday example

An outdoor reading event prepares a simple indoor alternative while the forecast is favourable, because the host has a suitable room available if conditions change.

When to use it

Use it when an easy, relevant precaution remains useful despite a favourable start.

Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.