Marketing sends what it believes are good enquiries. Sales calls the ones that look promising and gets on with the deals already in hand. Neither side is careless. The trouble is that nobody ever wrote down what a good enquiry is, who picks it up, or how quickly. So the same conversation repeats every month, with two versions of the same numbers, and the enquiry that mattered sits untouched in between.
Why it persists. The handoff sits between two owners, which usually means it has no owner. Marketing is measured on enquiries, sales on closures, and the gap between the two belongs to neither. Most SMBs run it on a verbal understanding that worked when the founder saw every lead. When volume grows, or a person leaves, the understanding does not travel. Buying a CRM does not fix it either, because software enforces rules only after somebody agrees what the rules are.
If it stays unresolved. The cost stays invisible, which is why it survives. You keep paying for enquiries that are never worked, keep reporting a conversion rate that is not real, and keep making budget decisions on it. As the team grows, the disagreement grows with it, and the first serious argument usually arrives in a quarter when the number is missed and neither side can prove what happened.