欠かす

1. Origins, structure, and basic meaning

• Structure: 欠かす, read かかす, means omitting something necessary or skipping a regular activity.
• Basic usage: It is used when discussing a regular morning walk or an omitted safety check.
  • 彼は忙しくても毎朝の散歩を欠かさない。

2. Common pitfalls and similar expressions

• Consistency expressed by the negative form
  • 欠かさない means consistently doing something without missing it. 欠かせない means that something is indispensable, emphasizing necessity rather than consistency.