When Should a Habit Change Instead of Just Trying Harder?

Say you planned a 20-minute reading session after work, but it keeps colliding with late meetings. Is the useful response to change the time, make the session smaller, or admit this may not be the right routine right now?

What evidence helps you choose? I’m interested in how people adjust a habit without treating every missed attempt as a personal failure—or adding so much structure that the habit becomes another burden.