In Plain English
Think of a crawler as a visitor following signposted paths through a building. Discovery gives the visitor an address or doorway; crawling is the act of requesting what is there and following accessible routes onwards. Normal internal links create useful routes. Access controls, broken links, server errors and resources a crawler cannot use may interrupt the journey. Reaching a page is only the visit: it does not guarantee that the page will be selected for the index.
Why it matters
A valuable guide cannot be evaluated if a search crawler cannot reliably reach and request it. Clear site navigation and useful internal links support both people and crawlers, while sensible technical access prevents accidental dead ends.
Crawlability is best checked as a route, not as an isolated URL. Start from a page people and crawlers already reach, follow the same links, and confirm that the destination and its essential resources respond normally. Sitemaps can complement these routes, but clear navigation makes the relationship visible to visitors too. When diagnosing a problem, distinguish “not discovered”, “not crawled yet” and “crawl attempt failed”; each points to a different next step.
Example
A crawler reaches a new guide by following a normal HTML link from the Learn hub.
Common misunderstanding
Submitting a sitemap does not force a search engine to crawl every listed URL immediately. A sitemap is a discovery aid, not an instant collection order.