What is the difference between a weak bullet point and a strong one?

A weak bullet is vague and describes a general duty; a strong bullet is specific, starts with an action and shows scope or results.

Weak: "Responsible for social media."
Strong: "Planned and posted daily content on Instagram and LinkedIn for a regional furniture brand, growing followers steadily over a year."

Weak: "Helped customers."
Strong: "Answered about 50 customer calls a day on billing and technical issues, resolving most on the first call."

Weak: "Did maintenance work."
Strong: "Carried out preventive maintenance on 12 chillers and AHUs in a hospital, following the monthly PPM schedule."

What made the difference:

• An action verb instead of "responsible for" or "helped".
• What exactly was done and for whom.
• Size, frequency or a result.